Merge pull request #7368 from cpcloud/fix-float-mixed

BUG/REG: fix float64index -> mixed float assignment
make nanops._maybe_null_out work with complex numbers ( issue #7353 )
support axis=None for nanmedian ( issue #7352 )
Make nanops._has_infs work for additional dtypes and multidimensional arrays ( issue #7357 )
add tests for nanops
minor nanops pep8 fixes
make nanops work when ndim==1 and axis==0 ( issue #7354 )