ENH: Inline check_and_adjust_index

The function takes a considerable amount of time of np.take and
to also fancy indexing. Simple np.takes can speed up by more then
40%, fancy indexes around 10%.
BUG: runtests: make -t option work again
Merge pull request #3947 from seberg/inline-check-index

ENH: Inline check_and_adjust_index
Merge pull request #3948 from pv/runtests-path

BUG: runtests: make -t option work again
MAINT: double underscores in Lapack-lite C module

Strictly speaking, any non-standard name with "__" in it causes
undefined behavior in C. It's also completely unnecessary to use
any in this module.
MAINT: C identifiers causing UB + useless char returns

C identifiers aren't allowed to match "^_[A-Z]". Fixed that in
numpyos.c and removed some more useless underscores.

Changed NumPyOS_ascii_tolower and the code that calls it to handle
ints, not chars. C promotes char to int in so many situations that
char variables are just a pain. (The C standard library uses int
in <ctype.h>, for example.)
MAINT: unused variable, formatting
MAINT: typo
MAINT: fix item_selection.c so it compiles without warnings
Merge pull request #3950 from larsmans/c-fixes

C fixes
ENH: unroll vector minmax loop

Improves speed by 10% on intel cpus.
Simplify code by moving the fenv support check into the dispatcher. fenv works
on all common platforms (including windows), the fallback is not worth it for
the exotic platforms where it might not be available.
ENH: accept callable as message in assert_

Allows deferring evaluation until failure.
Used for blocked minmax test which evaluate array representations for
the error message many thousand times accumulating to a full second
useless runtime.