BLD: Backport Ralf's gh-3766 fixes to the bento build scripts.

The original PR included fixes for ufunc_override that are not
needed for 1.8, so I just copied the files numpy/core/bento.info and
numpy/core/bscript from master.
Merge pull request #3784 from charris/backport-1.8-3766

Backport 1.8 3766