_mdb_get_database: Restore 'uri is db name' functionality.
_mdb_get_database: Restore 'uri is db name' functionality.

Forgot to run the test suite after the last round of changes :(.
On the good side, this commit should actually restore backwards
compatibility with previous MongoDB support.

tpazderka/pysaml2,tpazderka/pysaml2,Runscope/pysaml2,arbn/pysaml2,arbn/pysaml2,Runscope/pysaml2