BUG: get_info('openblas') does not read libraries key

The documented libraries tag in the site.cfg is not read by the configuration,
instead openblas_libs is used, this is inconsistent with atlas configuration.
So libraries first and then try openblas_libs for backward compatibility.

Also ensure check_libs returns None instead of a dict of empty lists if
nothing is found.
DOC: update openblas fork warning with fixed pthread build info
BUG: Fixes #2799
Use `np.sort` instead of `sorted` when the input is a list and no indices
are requested. Fixes #2799.
Fix seterr example for resetting to old settings
BUG: Fixed issue 3504, and added tests for complex support
ENH: hint that nelem == 1 branch is more likely

improves performance for simple takes by 10%, chunked takes spend more
time copying so the less dense code matters less.
DOC: some versionadded notes
DOC: assert_no_warnings versionadded 1.8 -> 1.7
Merge pull request #4390 from juliantaylor/backport-fixes3-1.8

Backport fixes to 1.8