ENH: stats: Add Mood's median test.

This test is described in many statistics text books.  Google for it and you'll find many descriptions and tutorials about it.  It's about time we had it in scipy.  Since we already have the contingency table code, the implementation is pretty simple.
`mood` tests for equal scale parameters, while `fligner` and `bartlett` (along with `levene`) are tests of equal variance, so these don't seem related enough to include in "See Also".  I'll add `kruskal` and `mannwhitneyu`  (see, for example, the start of the section "Applications and comparsion to other tests" at http://en.wikipedia.org/wiki/Median_test).