BUG: ensure raising of invalid on bad complex powers

put inf - inf into a volatile variable so it is not optimized away by
compilers.
BUG: fix bad alignment asserts

if the arrays are smaller than a vector they don't need to be aligned.
Merge pull request #3727 from juliantaylor/dbg-fixes-1.8.x

Backport PR 3726
BUG: f2py, fix decref on wrong object

missing brackets causes decref on an wrong object.
shows itself as abort with negative refcount in test_callback using
python-dbg.
Merge pull request #3729 from juliantaylor/f2py-negative-refcount-1.8.x

Backport PR 3728
MAINT: Make the qr raw mode test independent of the LAPACK library.

The qr factorization is not unique and the values returned by the raw
mode may differ between LAPACK versions. Consequently, the results
cannot be checked against known values.

Closes #3703.
BUG: fix zero initialization with subarray dtypes

closes #3724
Merge pull request #3734 from charris/backport-1.8-3723

Backport 1.8 3723
Merge pull request #3735 from juliantaylor/fix-subarray-zeros-1.8.x

Backport PR 3725