Merge pull request #4455 from juliantaylor/api-restore-1.8

restore npy_PyFile_Dup api for 1.8.x
BUG: Fix commutativity of {dot,multiply,inner}(scalar, matrix_of_objs)

Fixes #2469 and #4482. Relaxes fail condition to allow subtype as documented.
DOC: Add backport of gh-4483 to release notes.
Merge pull request #4501 from charris/backport-1.8-gh-4483

Backport 1.8 gh 4483
ENH: Backport scalarmathmodule.h.src from 1.9.0-devel.

This is needed in order to backport npyiter fixes.
BUG: Backport nditer fixes and tests.

This is mostly gh-4466, but other bits had to come with it to
make it work.
DOC: Document backport of gh-4466 in 1.8.1 release notes.