BLD: raise a clearer warning in case of building without cleaning up first.

Occurs only on Python 3.x when a version.py file is already present, due to
copying the whole tree into build/pyk3/.

(backport of cd6d53ff)
BLD: fix build for py3k + pip. Closes #1857. Thanks to Erik Bray.

Also works inside a virtualenv.
BLD: follow build_ext coding convention in build_clib to catch strange fcompiler value reported in ml.
BLD: fix up detection of Intel CPU on OS X in system_info.py.
BLD: add support for the new X11 directory structure on Ubuntu & co.
BUG: distutils: change compile flag on AIX from -O5 to -O3. See #1261.
BUG: distutils: update HP compiler flags. Closes #1377.
ENH: distutils: provide better support for C++ code on HPUX. Closes #1383.
FIX: add ufsparse to the libraries search path.

Fixes a build failure on macports when it detected umfpack but was
unable to build the extension module. Equivalent to the
'/usr/include/suitesparse' path under Debian.
ENH: Add 'pgfortran' as a valid compiler in the Portland Group
suite of fortran compilers. Adjust the version string command.
MAINT: update version match regexp for IBM AIX Fortran compilers.

The patched version correctly matches the output of ``xlf -qversion`` on my AIX platform:

  $ uname -a
  AIX c1t0101 3 5 00CF49B14C00
  $ xlf -qversion
  IBM XL Fortran for AIX, V12.1
  Version: 12.01.0000.0000
  $
Merge pull request #258 from rgommers/backport-build-fixes

Backport build fixes to 1.6.x
BUG: ticket #2063, make unique return consistent index.

Make unique use  mergesort when return_index is true. This quarantees that
the returned indices are of the first occurrence of the unique elements and
makes the behavior better defined and consistent.
BUG: ticket #1149, make argmin work for datetime.

Backport of 6fc0737 'ENH: Explicitly coded argmin for timedelta'
BUG: Fix maximum/minimum for object arrays in Python 3.

Use PyObject_RichCompareBool instead of PyObject_Cmp.
BUG: ticket #1138

This is a backport of 4daf949

PyArray_FromBuffer: Allow creating arrays from empty buffers
or empty slices.

That finally closed the ticket.
DOC: ticket #1446, correct note about correspondence vstack and
concatenate.
BUG: Ticket #1672 fix allclose to work for scalar inf.

Backport of 7497d60.

Also actually runs tests. Tests were not run before because the allclose
test class was a subclass of TestCase and used generators. This is not
supported by nose, tests will be skipped.

Also changes plain asserts to assert_().

Thanks to Justin Peel for the allclose inf fix.
ENH: ticket #1675, Add scalar support for the format() function.

Backport of 88e8c15.
BUG: ticket #1747, make np.median() work for 0-D arrays.