pip installation fails: Double requirement given: numpy==1.12.1...
Hello,

I have an issue with installation from current release on PyPi via pip:

In a fresh python3 virtualenv I do following, and it crashes on `Double requirement given: numpy==1.12.1 ...`:

```
(p3-sns) d@e:~/Plocha/mff/diplomka/fork2$ pip install pandas
Collecting pandas
  Downloading https://files.pythonhosted.org/packages/08/01/803834bc8a4e708aedebb133095a88a4dad9f45bbaf5ad777d2bea543c7e/pandas-0.22.0.tar.gz (11.3MB)
    100% |████████████████████████████████| 11.3MB 1.6MB/s 
  Installing build dependencies ... error
  Complete output from command /home/d/Plocha/mff/diplomka/fork2/p3-sns/bin/python3 -m pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-qp8xf9cn https://files.pythonhosted.org/packages/1b/d2/22cde5ea9af055f81814f9f2545f5ed8a053eb749c08d186b369959189a8/wheel-0.31.0-py2.py3-none-any.whl#sha256=9cdc8ab2cc9c3c2e2727a4b67c22881dbb0e1c503d592992594c5e131c867107 https://files.pythonhosted.org/packages/20/d7/04a0b689d3035143e2ff288f4b9ee4bf6ed80585cc121c90bfd85a1a8c2e/setuptools-39.0.1-py2.py3-none-any.whl#sha256=8010754433e3211b9cdbbf784b50f30e80bf40fc6b05eb5f865fab83300599b8 https://files.pythonhosted.org/packages/70/25/1e1521e6ce2cf78ff4a8b06fbc2cd513ce004ec337000eddfe016fdf3fc6/Cython-0.28.2-cp34-cp34m-manylinux1_x86_64.whl#sha256=85f7432776870d65639fed00f951a3c05ef1e534bc72a73cd1200d79b9a7d7d0 https://files.pythonhosted.org/packages/fc/1b/a1717502572587c724858862fd9b98a66105f3a3443225bda9a1bd16ee14/numpy-1.9.3-cp34-cp34m-manylinux1_x86_64.whl#sha256=bff36563f9d6a06a81ae232f49d2946c84c05e391a7dff057496033c79507860 https://files.pythonhosted.org/packages/02/64/c6c1c24ff4dbcd789fcfdb782e343ac23c074f6b8b03e818ff60eb0f937f/numpy-1.12.1-cp34-cp34m-manylinux1_x86_64.whl#sha256=4eac5f2f624c5e7eecbdb51395ff39a099c48cab607a158f16f288c6fe39a2b3 https://files.pythonhosted.org/packages/1b/ee/f65826b2880f67652c21326565b4c166c7cdb1019f84b82af65e625475cd/numpy-1.13.1-cp34-cp34m-manylinux1_x86_64.whl#sha256=838e48df3703c8747f355cd6386e0680b906a2f7b2bbd304e8a2d531692484ce:
  Double requirement given: numpy==1.12.1 from https://files.pythonhosted.org/packages/02/64/c6c1c24ff4dbcd789fcfdb782e343ac23c074f6b8b03e818ff60eb0f937f/numpy-1.12.1-cp34-cp34m-manylinux1_x86_64.whl#sha256=4eac5f2f624c5e7eecbdb51395ff39a099c48cab607a158f16f288c6fe39a2b3 (already in numpy==1.9.3 from https://files.pythonhosted.org/packages/fc/1b/a1717502572587c724858862fd9b98a66105f3a3443225bda9a1bd16ee14/numpy-1.9.3-cp34-cp34m-manylinux1_x86_64.whl#sha256=bff36563f9d6a06a81ae232f49d2946c84c05e391a7dff057496033c79507860, name='numpy')
  
  ----------------------------------------
Command "/home/d/Plocha/mff/diplomka/fork2/p3-sns/bin/python3 -m pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-qp8xf9cn https://files.pythonhosted.org/packages/1b/d2/22cde5ea9af055f81814f9f2545f5ed8a053eb749c08d186b369959189a8/wheel-0.31.0-py2.py3-none-any.whl#sha256=9cdc8ab2cc9c3c2e2727a4b67c22881dbb0e1c503d592992594c5e131c867107 https://files.pythonhosted.org/packages/20/d7/04a0b689d3035143e2ff288f4b9ee4bf6ed80585cc121c90bfd85a1a8c2e/setuptools-39.0.1-py2.py3-none-any.whl#sha256=8010754433e3211b9cdbbf784b50f30e80bf40fc6b05eb5f865fab83300599b8 https://files.pythonhosted.org/packages/70/25/1e1521e6ce2cf78ff4a8b06fbc2cd513ce004ec337000eddfe016fdf3fc6/Cython-0.28.2-cp34-cp34m-manylinux1_x86_64.whl#sha256=85f7432776870d65639fed00f951a3c05ef1e534bc72a73cd1200d79b9a7d7d0 https://files.pythonhosted.org/packages/fc/1b/a1717502572587c724858862fd9b98a66105f3a3443225bda9a1bd16ee14/numpy-1.9.3-cp34-cp34m-manylinux1_x86_64.whl#sha256=bff36563f9d6a06a81ae232f49d2946c84c05e391a7dff057496033c79507860 https://files.pythonhosted.org/packages/02/64/c6c1c24ff4dbcd789fcfdb782e343ac23c074f6b8b03e818ff60eb0f937f/numpy-1.12.1-cp34-cp34m-manylinux1_x86_64.whl#sha256=4eac5f2f624c5e7eecbdb51395ff39a099c48cab607a158f16f288c6fe39a2b3 https://files.pythonhosted.org/packages/1b/ee/f65826b2880f67652c21326565b4c166c7cdb1019f84b82af65e625475cd/numpy-1.13.1-cp34-cp34m-manylinux1_x86_64.whl#sha256=838e48df3703c8747f355cd6386e0680b906a2f7b2bbd304e8a2d531692484ce" failed with error code 1 in None
```

Can you fix it or hint me how to avoid this?

Thank you!
