Added ObjCSummaryCache, a new summary cache object to cache summaries for Objective-C methods.  Instead of mapping from Selectors -> Summaries, we will now map from (ObjCInterfaceDecl*,Selectors) -> Summaries.  This will allow more nuanced summary generation.  This patch just swaps in the new data structure; the rest of the code works as before by allowing the ObjCInterfaceDecl* to be null.

llvm-svn: 52653