This commit completes the rearchitecting of ClangASTSource

to allow variables in the persistent variable store to know
how to complete themselves from debug information.  That
fixes a variety of bugs during dematerialization of 
expression results and also makes persistent variable and
result variables ($foo, $4, ...) more useful.

I have also added logging improvements that make it much
easier to figure out how types are moving from place to 
place, and made some checking a little more aggressive.

The commit includes patches to Clang which are currently being
integrated into Clang proper; once these fixes are in Clang
top-of-tree, these patches will be removed.  The patches don't
fix API; rather, they fix some internal bugs in Clang's 
ASTImporter that were exposed when LLDB was moving types from
place to place multiple times.

llvm-svn: 144969