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.