Merge pull request #40 from fredrikt/67e3b7a8c289a2c861b4476753d6f367a3d258cc

small bugfix
Improve MongoDB support.

* Support configuration with MongoDB connection URI strings.
* Handle connecting to replica sets.
* Use standard notation database+collection rather than
  collection+sub_collection.

Note that these changes are NOT expected to be fully backwards
compatible for someone using mongodb with pysaml2 already.
New method for verifying that the assertion consumer servive actually belongs to the issuer of the AuthnRequest.
Merge branch 'master' of github.com:rohe/pysaml2
Merge branch 'mongodb_uri_support' of https://github.com/fredrikt/pysaml2
Merge branch 'master' of https://github.com/rohe/pysaml2
_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.