The `import_array()` macro, that defined a C code block that included a
return, was not handled correctly. The fix here is to cdef a replacement
`import_array` function with a defined error return. The new function is
a slight variation of the corresponding function defined by Cython.

The latest Cython came out and it causes the cythonized mtrand.c source
to issue a compile warning for Python 3, breaking NumPy travis tests. As
a temporary fix, force the tests to use Cython 0.26.

Python 3.6 added a private API for tracing arbitrary memory allocations
so the tracemalloc module [0] can be used with numpy.

closes gh-4663

[0] https://docs.python.org/3/library/tracemalloc.html

MAINT: Remove numpy-macosx-installer and win32build directories.

BLD: rewrite np.distutils.exec_command.exec_command()

The scripts in those directories were used to build windows superpacks
and mac dmg files. We now release wheels for both of those platforms.
There is little overhead maintaining these scripts, but they are clutter
and will eventually bit rot if not used for current systems. So remove
them.

Make the code a bit cleaner.

Fix the escape sequences deprecated in Python 3.6 found in the
tools directory. Note that this does not include the files in
tools/swig/tests which are not even Python 3 compatible at this point.

Python 3.6 deprecates a number of escaped characters that were accepted
before. For instance, '\(' was previously accepted but must now be
written as '\\(' or r'\('.

[ci skip]

newer gcc, python, cython...
update eatmydata setting for new paths and earlier usage during chroot setup