Merge pull request #7427 from toddrjen/nantest

add unit tests for nanops
make nanops._maybe_null_out work with complex numbers ( issue #7353 )
make nanops work when ndim==1 and axis==0 ( issue #7354 )
make nanops work when ndim==1 and axis==0 ( issue #7354 )
support axis=None for nanmedian ( issue #7352 )