Transformation-Callback Pipeline for Decls needing special handling
(when defining after being forward declared.)

New state in Interpreter (AutoloadingStateInfo) containing a map.
AutoloadingTransform adapted to push required decls into this map.
AutoloadCallback adapted to be called when a file is included (but before being parsed)
(done by enabling PPCallbacks and overriding InclusionDirective method)
m_PPCallbacks changed from OwningPtr to a normal pointer as an workaround for double free bug.
Default template arguments as a POC example usage of this pileline.

Test:
AutoForwarding.C now passes because of this commit.

Extra:
Re-enabled the printing of class template default arguments when generating fwd declarations.
Forward declprinter now looks up the SourceManager for file name instead of directly printing the Argument.