Fix race condition in WebConnectionStream

See https://bugzilla.xamarin.com/show_bug.cgi?id=1553
[man] update Mono version from "2.11" to "3.0"
[WebConfigurationManager] Fix memleak by using a LruCache (BXC#5598)

System.Web.ConfigurationManager had a cache which didn't have any max limit,
therefore when using Restful URIs in ASP.NET (like having some variable
parameter in the virtual path, i.e. /user/{userId}/tracks, where {userId}
is a variable Integer) this was very likely to cause a leak which would
end up causing troubles, like an InvalidCastException thrown by
HttpApplication::PreStart()

(Read operations in the cache now cause a write operation on the cache
object, so all sectionCache lock-read usages are converted to lock-write.)

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=5598
Update to 3.0.12
Avoid the class name check in is_async_state_machine_class (), csc seems to generate a different name. Fixes #12329.
Implement Task::AsyncWaitHandle. Fixes #12342
Add the hostname into the exception message when doing dns lookups.
[xbuild]: Fix 'make test'.
[xbuild]: Fix task batching for <ItemGroup> inside <Target>.

This fixes

	<Target Name="Simple">
		<ItemGroup>
			<Foo Include="A;B" />
			<All Include="%(Foo.Identity)" />
		</ItemGroup>
		<Message Text="ALL: @(All)" />
	</Target>
[make]: Build Facade assemblies in mcs/class/lib/$(PROFILE)/Facades.
Ooops, variance is not available in 3.5.
Share a bit more code wrt OID/hash so X.509 CRL can use any of them (like the certificates) and make the code a little bit more linker friendly
[xbuild]: Fix reference assembly path.
[xbuild]: Provide a real Microsoft.Portable.CSharp.targets
[xbuild]: Implicitly expand PCL2 facade assemblies.

* GetReferenceAssemblyPaths: return the reference assemblies for the
  requested PCL profile.

* ResolveAssemblyReference: always include System.Runtime as a
  dependency; the .targets check for this to determine whether
  we're a PCL2 library.
Add Microsoft.Portable.CSharp.targets to the .spec file.
[System.Drawing]: Disable broken tests.
Add missing MSBuild Framework interface.
Add some missing MSBuild project model evaluation members.
Refactor the [D|R]SACryptoServiceProvider constructors so it's possible for the linker to remove the dependency on the XML parser when CspParameters are not used (saves 42KB)