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
Merge pull request #4191 from juliantaylor/openblas-info

BUG: get_info('openblas') does not read libraries key
Fix infinite recursion when initializing sub-class of array scalars.
Add test-case for multiple-inheritance on an array-scalar.
Merge pull request #4375 from ContinuumIO/fix_scalar_inherit

Fix scalar inherit
DOC: some versionadded notes
DOC: assert_no_warnings versionadded 1.8 -> 1.7
Merge pull request #4383 from argriffing/more-versionadded

DOC: some versionadded notes
ENH: Make output of get_atlas_info conditional on system_info.verbosity