Don't verify mutability of value types in imported assemblies. Should fix #289
Update mscorlib.js

In the case of a Web Worker, window is undefined, in which case set window to the Web Worker's 'global scope' self.
Update mscorlib.js

when global is undef, try setting it first to window, then to self (if window is not available)
.Net compatibility fixes regarding tasks that throw:

1. Always wrap the call to a TaskCompletionSource.SetException() in an AggregateException (even when the argument was already an AggregateException,
2. Implement AggregateException.Flatten(),
3. Awaiting a task now throws the inner exception (#294)
Merge pull request #293 from kenneyw/patch-1
Release 2.5.0
Merge branch 'master' into develop