importing pandas breaks after successfully installing pandas with pip
#### Code Sample, a copy-pastable example if possible

```bash
> docker run --tty --interactive --rm python:2.7.12-alpine ash
/ # apk update
fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/community/x86_64/APKINDEX.tar.gz
v3.4.6-150-gf952adf [http://dl-cdn.alpinelinux.org/alpine/v3.4/main]
v3.4.6-83-g67e50bc [http://dl-cdn.alpinelinux.org/alpine/v3.4/community]
OK: 5983 distinct packages available
/ # apk add cython g++ musl-dev
(1/21) Upgrading musl (1.1.14-r12 -> 1.1.14-r14)
(2/21) Installing libffi (3.2.1-r2)
(3/21) Installing python (2.7.12-r0)
(4/21) Installing cython (0.24-r1)
(5/21) Installing libgcc (5.3.0-r0)
(6/21) Installing libstdc++ (5.3.0-r0)
(7/21) Installing binutils-libs (2.26-r1)
(8/21) Installing binutils (2.26-r1)
(9/21) Installing gmp (6.1.0-r0)
(10/21) Installing isl (0.14.1-r0)
(11/21) Installing libgomp (5.3.0-r0)
(12/21) Installing libatomic (5.3.0-r0)
(13/21) Installing pkgconf (0.9.12-r0)
(14/21) Installing pkgconfig (0.25-r1)
(15/21) Installing mpfr3 (3.1.2-r0)
(16/21) Installing mpc1 (1.0.3-r0)
(17/21) Installing gcc (5.3.0-r0)
(18/21) Installing musl-dev (1.1.14-r14)
(19/21) Installing libc-dev (0.7-r0)
(20/21) Installing g++ (5.3.0-r0)
(21/21) Upgrading musl-utils (1.1.14-r12 -> 1.1.14-r14)
Executing busybox-1.24.2-r11.trigger
OK: 230 MiB in 51 packages
/ # ln -s locale.h /usr/include/xlocale.h
/ # pip install numpy==1.11.3 pandas==0.20.2
Collecting numpy==1.11.3
  Downloading numpy-1.11.3.zip (4.7MB)
    100% |████████████████████████████████| 4.7MB 242kB/s 
Collecting pandas==0.20.2
  Downloading pandas-0.20.2.tar.gz (10.3MB)
    100% |████████████████████████████████| 10.3MB 124kB/s 
Collecting python-dateutil (from pandas==0.20.2)
  Downloading python_dateutil-2.6.0-py2.py3-none-any.whl (194kB)
    100% |████████████████████████████████| 194kB 994kB/s 
Collecting pytz>=2011k (from pandas==0.20.2)
  Downloading pytz-2017.2-py2.py3-none-any.whl (484kB)
    100% |████████████████████████████████| 491kB 874kB/s 
Collecting six>=1.5 (from python-dateutil->pandas==0.20.2)
  Downloading six-1.10.0-py2.py3-none-any.whl
Building wheels for collected packages: numpy, pandas
  Running setup.py bdist_wheel for numpy ... done
  Stored in directory: /root/.cache/pip/wheels/8f/d6/97/4cc26777ee05997164e480e2e5de2c9e9c4e32dfe325ea5bd6
  Running setup.py bdist_wheel for pandas ... done
  Stored in directory: /root/.cache/pip/wheels/fc/fd/0a/5857e8bee7d5cc3ca22228fb7ab5efa43be57c0f9103e54098
Successfully built numpy pandas
Installing collected packages: numpy, six, python-dateutil, pytz, pandas
Successfully installed numpy-1.11.3 pandas-0.20.2 python-dateutil-2.6.0 pytz-2017.2 six-1.10.0
You are using pip version 8.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
/ # python -c "import pandas"
RuntimeError: module compiled against API version 0xb but this version of numpy is 0xa
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/pandas/__init__.py", line 35, in <module>
    "the C extensions first.".format(module))
ImportError: C extension: umpy.core.multiarray failed to import not built. If you want to import pandas from the source directory, you may need to run 'python setup.py build_ext --inplace --force' to build the C extensions first.
```
#### Problem description

Installing Pandas with `pip` is successful, but `import pandas` breaks.

If I issue two separate `pip install` commands, one for `numpy` and one for `pandas`, it works:
```bash
> docker run --tty --interactive --rm python:2.7.12-alpine ash
/ # apk update
fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.4/community/x86_64/APKINDEX.tar.gz
v3.4.6-150-gf952adf [http://dl-cdn.alpinelinux.org/alpine/v3.4/main]
v3.4.6-83-g67e50bc [http://dl-cdn.alpinelinux.org/alpine/v3.4/community]
OK: 5983 distinct packages available
/ # apk add cython g++ musl-dev
(1/21) Upgrading musl (1.1.14-r12 -> 1.1.14-r14)
(2/21) Installing libffi (3.2.1-r2)
(3/21) Installing python (2.7.12-r0)
(4/21) Installing cython (0.24-r1)
(5/21) Installing libgcc (5.3.0-r0)
(6/21) Installing libstdc++ (5.3.0-r0)
(7/21) Installing binutils-libs (2.26-r1)
(8/21) Installing binutils (2.26-r1)
(9/21) Installing gmp (6.1.0-r0)
(10/21) Installing isl (0.14.1-r0)
(11/21) Installing libgomp (5.3.0-r0)
(12/21) Installing libatomic (5.3.0-r0)
(13/21) Installing pkgconf (0.9.12-r0)
(14/21) Installing pkgconfig (0.25-r1)
(15/21) Installing mpfr3 (3.1.2-r0)
(16/21) Installing mpc1 (1.0.3-r0)
(17/21) Installing gcc (5.3.0-r0)
(18/21) Installing musl-dev (1.1.14-r14)
(19/21) Installing libc-dev (0.7-r0)
(20/21) Installing g++ (5.3.0-r0)
(21/21) Upgrading musl-utils (1.1.14-r12 -> 1.1.14-r14)
Executing busybox-1.24.2-r11.trigger
OK: 230 MiB in 51 packages
/ # ln -s locale.h /usr/include/xlocale.h
/ # pip install numpy==1.11.3 
Collecting numpy==1.11.3
  Downloading numpy-1.11.3.zip (4.7MB)
    100% |████████████████████████████████| 4.7MB 221kB/s 
Building wheels for collected packages: numpy
  Running setup.py bdist_wheel for numpy ... done
  Stored in directory: /root/.cache/pip/wheels/8f/d6/97/4cc26777ee05997164e480e2e5de2c9e9c4e32dfe325ea5bd6
Successfully built numpy
Installing collected packages: numpy
Successfully installed numpy-1.11.3
You are using pip version 8.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
/ # pip install pandas==0.20.2
Collecting pandas==0.20.2
  Downloading pandas-0.20.2.tar.gz (10.3MB)
    100% |████████████████████████████████| 10.3MB 125kB/s 
Collecting python-dateutil (from pandas==0.20.2)
  Downloading python_dateutil-2.6.0-py2.py3-none-any.whl (194kB)
    100% |████████████████████████████████| 194kB 787kB/s 
Collecting pytz>=2011k (from pandas==0.20.2)
  Downloading pytz-2017.2-py2.py3-none-any.whl (484kB)
    100% |████████████████████████████████| 491kB 1.0MB/s 
Requirement already satisfied (use --upgrade to upgrade): numpy>=1.7.0 in /usr/local/lib/python2.7/site-packages (from pandas==0.20.2)
Collecting six>=1.5 (from python-dateutil->pandas==0.20.2)
  Downloading six-1.10.0-py2.py3-none-any.whl
Building wheels for collected packages: pandas
  Running setup.py bdist_wheel for pandas ... done
  Stored in directory: /root/.cache/pip/wheels/fc/fd/0a/5857e8bee7d5cc3ca22228fb7ab5efa43be57c0f9103e54098
Successfully built pandas
Installing collected packages: six, python-dateutil, pytz, pandas
Successfully installed pandas-0.20.2 python-dateutil-2.6.0 pytz-2017.2 six-1.10.0
You are using pip version 8.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
/ # python -c "import pandas"
```
