Added release notes for 1.6.1.
BUMP 1.6.1.4678
versioning GlobalAssemblyInfo for next release.
CSHARP-614, CSHARP-615: Added MongoClient and replaced SafeMode with WriteConcern and related changes.
Improved wording of error messages and changed WValue so no new subclasses can be created.
CSHARP-610 Invalid server address message.

Fixes the FormatException message in the path in
MongoServerAddress::Parse where the provided 'url' does not pass
the ::TryParse criteria for correctness. The intent was to provide
the offending value in the message, but the developer forgot to
fill in the {0} placeholder.
CSHARP-610: merged pull request 134 and added more unit tests.
CSHARP-614, CSHARP-615: better unit tests.
CSHARP-606: added support for type discriminated queries on fields.
CSHARP-578: added contributing doc.
added AllClassMaps - to enable us to get all the currently registered class maps out of BsonClassMap
CSHARP-628: added support for enumerating the registered class maps.
Added ToLowerInvariant ToUpperInvariant

Added ToLowerInvariant and ToUpperInvariant string methods to the
recognized linq string methods
Unit tests for ToLowerInvariant, ToUpperInvariant

Unit tests were added for the invariant versions of the linq string
methods.
CSHARP-629: add support for ToLowerInvariant and ToUpperInvariant in linq queries.
CSHARP-627: remove FireAndForget keyword.
test readonly enabled.
CSHARP-627: Remove use of safe=true (still accepted on connection string for backward compatibility). Standardize on Acknowledged and Unacknowledged as the names of the WriteConcern constants for w=1 and w=0. Get unit tests to pass again.
CSHARP-614: Remove GetDatabase method from MongoClient (use GetDatabase in MongoServer instead).
Minor changes for 1.7.