asv ImportError
#### Code Sample, a copy-pastable example if possible
Clone and build pandas-dev, then from `pandas/asv_bench` do
```
asv continuous -f 1.1  upstream/master
```

#### Problem description

This yields an `ImportError` on my machine:
```
File "/pandas/asv_bench/benchmarks/gil.py", line 3, in <module>
from pandas import (DataFrame, Series, rolling_median, rolling_mean,
ImportError: cannot import name 'rolling_median'
```

Full stacktrace:

```
$ asv continuous -f 1.1  upstream/master 
· Creating environments
· Discovering benchmarks
·· Uninstalling from conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt.
·· Building 3597de0a for conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt.....................................................................
·· Installing into conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt..
·· Error running /Users/joerg/Documents/Github/pandas/asv_bench/env/83b3be1235aa7b08e8a17448e2f70790/bin/python /Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py discover /Users/joerg/Documents/Github/pandas/asv_bench/benchmarks /var/folders/27/qrg706z54l76vk7t__l43h140000gn/T/tmp6ldll0ln
             STDOUT -------->

             STDERR -------->
             Traceback (most recent call last):
               File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py", line 867, in <module>
                 commands[mode](args)
               File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py", line 812, in main_discover
                 list_benchmarks(benchmark_dir, fp)
               File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py", line 797, in list_benchmarks
                 for benchmark in disc_benchmarks(root):
               File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py", line 696, in disc_benchmarks
                 for module in disc_files(root, os.path.basename(root) + '.'):
               File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py", line 648, in disc_files
                 module = import_module(package + filename)
               File "/Users/joerg/Documents/Github/pandas/asv_bench/env/83b3be1235aa7b08e8a17448e2f70790/lib/python3.6/importlib/__init__.py", line 126, in import_module
                 return _bootstrap._gcd_import(name[level:], package, level)
               File "<frozen importlib._bootstrap>", line 994, in _gcd_import
               File "<frozen importlib._bootstrap>", line 971, in _find_and_load
               File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
               File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
               File "<frozen importlib._bootstrap_external>", line 678, in exec_module
               File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
               File "/Users/joerg/Documents/Github/pandas/asv_bench/benchmarks/gil.py", line 3, in <module>
                 from pandas import (DataFrame, Series, rolling_median, rolling_mean,
             ImportError: cannot import name 'rolling_median'
Traceback (most recent call last):
  File "/Users/joerg/anaconda3/bin/asv", line 11, in <module>
    load_entry_point('asv==0.3.dev1214+4112e36d', 'console_scripts', 'asv')()
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/main.py", line 38, in main
    result = args.func(args)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/commands/__init__.py", line 48, in run_from_args
    return cls.run_from_conf_args(conf, args)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/commands/continuous.py", line 61, in run_from_conf_args
    quick=args.quick, **kwargs
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/commands/continuous.py", line 86, in run
    _returns=run_objs, _machine_file=_machine_file)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/commands/run.py", line 192, in run
    commit_hashes, regex=bench)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmarks.py", line 369, in discover
    benchmarks = cls._disc_benchmarks(conf, repo, environments, commit_hash)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmarks.py", line 417, in _disc_benchmarks
    dots=False)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/plugins/conda.py", line 169, in run
    return self.run_executable('python', args, **kwargs)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/plugins/conda.py", line 175, in run_executable
    return super(Conda, self).run_executable(executable, args, **kwargs)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/environment.py", line 573, in run_executable
    return util.check_output([exe] + args, **kwargs)
  File "/Users/joerg/anaconda3/lib/python3.5/site-packages/asv/util.py", line 590, in check_output
    raise ProcessError(args, retcode, stdout, stderr)
asv.util.ProcessError: Command '/Users/joerg/Documents/Github/pandas/asv_bench/env/83b3be1235aa7b08e8a17448e2f70790/bin/python /Users/joerg/anaconda3/lib/python3.5/site-packages/asv/benchmark.py discover /Users/joerg/Documents/Github/pandas/asv_bench/benchmarks /var/folders/27/qrg706z54l76vk7t__l43h140000gn/T/tmp6ldll0ln' returned non-zero exit status 1
```

