* added readwritelock that properly supports async/await
* RavenDB-865 test passing
Merge branch 'New3' of github.com:ayende/ravendb into New3
make AsyncReaderWriterLock compile with Silverlight
proper fix for DateTimeOffsetIssues unit test
minor fixes related to RavenDB_1007 (also passes with Voron)
AttachmentContentType tests are passing (attachment metadata now overwrites matching http headers)
Merge branch 'New3' of github.com:ayende/ravendb into New3

Conflicts:
	Raven.Abstractions/Json/Linq/Extensions.cs