As part of the work to make Objective-C type information

from symbols more accessible, I have added a second
map to the ClangASTImporter: the ObjCInterfaceMetaMap.
This map keeps track of all type definitions found for
a particular Objective-C interface, allowing the
ClangASTSource to refer to all possible sources when
looking for method definitions.

There is a bug in lookup that I still need to figure out,
but after that we should be able to report full method
information for Objective-C classes shown in symbols.

Also fixed some errors I ran into when enabling the maps
for the persistent type store.  The persistent type store
previously did not use the ClangASTImporter to import
types, instead using ASTImporters that got allocated each
time a type needed copying.  To support the requirements
of the persistent type store -- namely, that types must be
copied, completed, and then completely severed from their
origin in the parser's AST context (which will go away) --
I added a new function called DeportType which severs all
these connections.

llvm-svn: 145914