Make project names compatible with TweetSharp refs

Renamed the .net20, net35 and clientprofile projects to use the project
names referenced in the TweetSharp repository. This should allow cloning
Hammock directly under the Tweetsharp clone and having the project
reference line up.
Modifications to remove compiler warnings.

MockHttpWebRequest modified so WP has "new"  ContentLength property and
other platforms have override (Silverlight 4 seems to have overridable
property and compiler complains if not overridden/new used).

WebQuery.Async - moved code and added try/catch to ensure response
disposed in case of unexpected exception. Existing code would change
variable referenced by using statement within the using block (if the
response needed uncompressing), which only disposed the original
response stream not the outer, and created a compiler warning.
Fix Hammock solution so it references changed project names.
Fix build problems in Mono project.