MAINT: fix some compiler warnings

implicit declarations, wrong declarations, unused variables and fixes a
comparison typo bug in multiarraymodule.c
Merge pull request #3362 from juliantaylor/compiler-warnings

MAINT: fix some compiler warnings
ENH: vectorize sqrt ufunc using SSE2

specialize the sqrt ufunc for float and double and vectorize it using
SSE2.

improves performance by 4/2 for float/double if one is not memory bound
due to non-cached data.
performance is always better on all tested machines (amd phenom X2,
intel xeon 5xxx/7xxx, core2duo, corei7)

This version will not set errno on invalid input, but numpy only checks
the fpu flags so the behavior is the same.

In principle the compiler could autovectorize it when setting ffast-math
(for no errno) and specializing the loop for the vectorizable strides
and giving it some hints (restrict, __builtin_assume_aligned, etc.),
but its simpler and more reliable to simply vectorize it by hand.
MAINT: use sse header macros for einsum sse activation
Merge pull request #3341 from juliantaylor/sse2-sqrt

vectorize sqrt ufunc with SSE2
BUG: set filename to None for memmaps of unnamed files

Closes gh-3302
DOC: Correcting docstring for asscalar
Merge pull request #3365 from juliantaylor/memmap-int-name

BUG: set filename to None for memmaps of unnamed files
BUG: fix leak and possible null dereference
TST: rename one test_hypergeometric_range function

There are two test functions named `test_hypergeometric_range`
Merge pull request #3372 from juliantaylor/datetime-leak

BUG: fix leak and possible use after free
TST: remove docstring from test_randint_range function

See doc/TESTS.rst.txt for the reason.
Merge pull request #3374 from cgohlke/patch-4

TST: rename 2nd test_hypergeometric_range function
Merge pull request #3366 from dnmiller/doc-fix

DOC: Correcting docstring for asscalar
BUG: Fix multivariate_normal issue with 'size' argument

Ensure that the multivariate_normal size argument can be a numpy integer. Add regression test. Apply PEP8 to test_regression.py. Regenerate mtrand.c.
TST: remove docstrings from test_ functions

See doc/TESTS.rst.txt for the reason.
Merge pull request #3373 from cgohlke/multivariate_normal-fix

multivariate_normal issue with 'size' argument
ENH: implement may_share_memory in C

memmap needs to call it in __array_finalize__ to determine if it can
drop the references on copies.
The python version if may_share_memory caused significant slowdowns when
slicing these maps.

closes gh-3364
ENH: improve performance of byte_bounds for continous arrays
MAINT: remove duplicated array extent calculation