CSHARP-889: using new createIndexes commands when talking with a 2.6 server.
changing all tests calling EnsureIndex to CreateIndex as EnsureIndex is now deprecated.
changed the name of AllowDiskUsage to AllowDiskUse.
allowing Windows 2003 to side-step the GSSAPI RFC.
CSHARP-899: added support for GSSAPI cross-realm authentication.
fixing tests against 2.6
fixing geo nears tests against 2.6
fixed text index test for server 2.6.
Relaxed some unit test assertions that were failing because different versions of the server were returning different error codes and messages.