BUG: fix bug in mstats.kurtosistest

Deleted astype(), because it is not an attribute of int (which could
be returned instead of an ndarray).
BUG: fix several bugs in the mstats normality tests.

Also provide decent test coverage.
TST: clean up test_mstats_basic.py for docstrings in tests
BUG: fix errors in mstats.ttest_rel and mstats.ttest_ind.

Change default of axis kw to 0 in ttest_rel.  This is OK without warning
because the function didn't work before anyway.

Also provide basic test coverage (comparison against nonmasked version).
Testing with various masked array inputs to be done.

Closes gh-3047.
BUG: fix issues in mstats.ttest_1samp.  Add axis keyword.
TST: normality tests: add a couple of tests for stats vs mstats
Merge pull request #3008 from rgommers/pull-2673

Fix mstats.kurtosistest, and test coverage for skewtest/normaltest