Fix:

<rdar://problem/6914474> checker doesn't realize that variable might
have been assigned if a pointer to that variable was passed to another
function via a structure

The problem here was the RegionStoreManager::InvalidateRegion didn't
invalidate the bindings of invalidated regions.  This required a
rewrite of this method using a worklist.

As part of this fix, changed ValueManager::getConjuredSymbolVal() to
require a 'void*' SymbolTag argument.  This tag is used to
differentiate two different symbols created at the same location.

llvm-svn: 82920