removed signal exception handlers for amd64.  need to investigate why we did this, and if it can be restored to reduce upstream divergence.

Implement relaxation of CoreCLR.  If the target of what you're trying to do is not platform code, we will allow the operation, where silverlight and moonlight will deny it

make it possible for an embedding app to provide its own mdb file, by not rejecting it if we already loaded a dummy debug module. Need to upstream this.

Suggested changes by gonzalo to make the mono runtime not crash when unloading a domain that uses the threadpool.  need to check if this is actually in upstream