Fixed a problem where persistent variables did

not correctly store the contents of Objective-C
classes.  This was due to a combination of
factors:

  1) Types were only being completed if we were
     looking inside them for specific ivars
     (using FindExternalVisibleDeclsByName). 
     We now look the complete type up at every
     FindExternalLexicalDecls.

  2) Even if the types were completed properly,
     ValueObjectConstResult overrode the type
     of every ValueObject using the complete type
     for its class from the debug information.
     Superclasses of complete classes are not
     guaranteed to be complete.  Although "frame
     variable" uses the debug information,
     the expression parser does now piece together
     complete types at every level (as described
     in Bullet 1), so I provided a way for the
     expression parser to prevent overriding.

  3) Type sizes were being miscomputed by
     ClangASTContext.  It ignored the ISA pointer
     and only counted fields.  We now correctly
     count the ISA in the size of an object.

<rdar://problem/12315386>

llvm-svn: 164333