BLD: fix Bento build.

Issue was introduced with PR-3524, the ufunc override stuff.
BLD: add new test extensions (rational, struct_ufunc, operand_flag) to Bento build.
TST: exercise median of median of 5 code by using a median of 3 killer dataset
ENH: remove an always true conditional

v[1] < v[2] is guaranteed by the swapping a few lines above
BUG: make checking for sse intrinsics more robust

check for two intrinsics from [ex]mmintrin.h instead of only checking
the existance of the headers.
E.g. mingw 4.2 emmintrin.h can be included even if SSE2 is disabled.
closes #3760
DOC: [bento] document that adding optional GCC performance improvements is TODO

[ci skip]
BUG: core: don't ignore raised exceptions in __numpy_ufunc__ handler
REF: core: clean up PyUFunc_CheckOverride

Move argument normalization out from the inner loop, reduce complexity.
Add error checks.
Merge pull request #3777 from pv/ufunc-override-fix

BUG: core: don't ignore raised exceptions in __numpy_ufunc__ handler
Merge pull request #3767 from juliantaylor/mom5-improve

Mom5 selection improvements
ENH: Added test cases for relation operation. To ensure behaviour of int. There is a need to add test case which ensure and maintain the behaviour of integer. As per pr #3567, which speed up integer scalar's operations by avoiding the conversion of integer to NumPy Scalar.
scalar relational operation
Moved test_multiarra_relational_operators to test_multiarray.py
fix indentation and nitpicks
Merge branch 'gh-3754'

* gh-3754:
  fix indentation and nitpicks
  Moved test_multiarra_relational_operators to test_multiarray.py
  scalar relational operation
  ENH: Added test cases for relation operation. To ensure behaviour of int. There is a need to add test case which ensure and maintain the behaviour of integer. As per pr #3567, which speed up integer scalar's operations by avoiding the conversion of integer to NumPy Scalar.
ENH: core: add a fast path for PEP3118 buffer string parsing

The call back to Python numpy.core._internal._dtype_from_pep3118 is an
unnecessary large overhead for the most common case, when the buffer
passed in has a simple non-composite type.

This commit adds a fast path for the simple case.
Merge pull request #3779 from pv/pep3118-fastpath

ENH: core: add a fast path for PEP3118 buffer string parsing
Merge pull request #3772 from juliantaylor/sse-configure-check

BUG: make checking for sse intrinsics more robust
TST: wrong indent in multiarray tests
Merge pull request #3781 from seberg/test_multiarray-indent

TST: wrong indent in multiarray tests