[PATCH] Simplify microsoft mangling of template instantiations

[Timur Iskhodzhanov]

The change looks good -- it simplifies the code and makes it faster.

David,
Do you have a good way to make sure we don't regress other than commit-and-see-if-it-explodes?

================
Comment at: lib/AST/MicrosoftMangle.cpp:678
@@ +677,3 @@
+    if (Found == NameBackReferences.end()) {
+      Out << BackReferenceKey;
+      if (NameBackReferences.size() < 10) {
----------------
This variable is no longer used as just a key.
Please use something like `TemplateMangling` or `TDMangling` instead?

http://reviews.llvm.org/D3983