DOC: Update docs to reflect deprecation of alterdot and restoredot.

Also move docstrings into the versions in numpy/core/numeric.py as
the functions are no longer in the defunct _dotblas module.
TST: Add vdot tests, move tests from test_blasdot to test_multiarray.

Not all tests from test_blasdot were relevant, as they checked the cblas
implementations against the non-cblas implementations. Those two are no
longer separate.

Remove test_blasdot.py as there nothing is left in it.