ENH: added functionality nanmedian to numpy

Implemented a nanmedian and associated tests as an
extension of np.median to complement the other
nanfunctions

Added negative values to the unit tests

Cleaned up documentation of nanmedian
Fix for #4655: Make fftpack._raw_fft threadsafe
BUG: cythonize sources for wheel build

Wheel build was not cythonizing sources, giving a compile error because
needed `numpy/random/mtrand/mtrand.c` was missing.
ENH: add small memory chunk cache

Add very simplistic caching of small memory blocks (< 1024 bytes)
This improves the performance of small array operations by about 15%-20%:

without cache:
In [1]: d = np.array([1,1])
In [2]: %timeit d*d*d*d
1000000 loops, best of 3: 2.1 µs per loop

with cache:
In [1]: d = np.array([1,1])
In [2]: %timeit d*d*d*d
1000000 loops, best of 3: 1.7 µs per loop

The cache is a simple list of buckets of pointers, one for each size up
to 1023 bytes.
Two caches are required one for array data one one for
dimensinos/strides as they use different allocators.
All pointers can still be deleted with their matching deallocator but
this implies the size of the block must be known at the time of the free
in order to place the pointer in the right bucket. This should not be an
issue for well behaved numpy users.

Technically the ABI is broken in this change as the size of the
dimension memory block has been decreased from 3 * nd to 2 * nd, the
increase to 3 was a relic from the NA branch and is not needed anymore.
It should be unlikely someone relies on this size.
TST: add travis test for wheel build and install

Add travis build that builds and installs wheel, runs tests from
installed wheel.
ENH: release GIL for callocs

useful for programs that block operations to avoid hitting the memory
bandwidth wall.
BUG: Fix test error in scipy introduced by commit d8fd283.

Revert "ENH: ma.asarray() and ma.asanyarray() will pass through input
        of the correct type."

This reverts commit d8fd28389adb491e24b7cdc25cd1b20f539310c3.

That commit caused test errors in scipy, which was apparently
expecting a copy rather than a passed through array. The idea
may be good, but at a minimum it should probably be preceded
by a deprecation period.

Closes #4675.
Merge pull request #4677 from charris/revert-d8fd283

BUG: Fix test error in scipy introduced by commit d8fd283.
MAINT: move memory allocator functions to own file alloc.c
Merge pull request #4606 from juliantaylor/small-memcache

ENH: add small memory chunk cache
MAINT: Remove deprecated importall.

The importall function was the only function in the numpytest.py
file, so remove the whole file.
DOC: Update the release notes.

Remove duplicated "New Features" heading.
Note removal of numpytesting.py file containing importall function.
Add comments to clarify cache handling in _raw_fft
MAINT:Ignore boolean '-' deprecation warnings in nosetester.py

This allows numpy 1.9 testing to be used with current scipy
without flooding the output with deprecation warnings.

The deprecation warnings are currently issued for both the
subtract and negative operators when used with booleans.
Merge pull request #4307 from dfreese/feature/nanmedian

ENH: added functionality nanmedian to numpy
Added regression tests for #4655
DOC: update 1.9.0-notes.
BUG: Add @DEFINE_NPY_RELAXED_STRIDES_CHECKING@ to _numpyconfig.h.in.

The entry is needed for Bento builds to correctly configure numpy.
Merge pull request #4682 from charris/fix-_numpyconfig.h.in

BUG: Add @DEFINE_NPY_RELAXED_STRIDES_CHECKING@ to _numpyconfig.h.in.
Make TestFFTThreadSafe tests Py3-compatible