[T4] Fix CompilerError ctor args in base template

Tested to match VS T4 engine.

BXC21691 - T4 null-reference usage for fileName when creating a
CompilerError object crashes CompilerError.ToString in the .NET framework
[AspNet] Fix type resolution when multiple registrations use same prefix

BXC21885 - UpdatePanel incorrectly added to the designer
as System.Web.UI.Webcontrols.UpdatePanel
[AspNet] Add some built-in control registrations
Fixed 'Bug 21898 - System.AggregateException: One or more errors
occured'.
I added some more exception checks to find errors in the assembly
browser more easily in the future. This particular one was caused by
calling a gtk method from a background thread.
[Ide] Fixed a bug in the type system assembly caching.
Merge branch 'master' into ios8