Store: (static analyzer)

- Change definition of store::Region and store::Binding (once again) to make
  them real classes that just wrap pointers. This makes them more strictly
  typed, and allows specific implementations of Regions/Bindings to just
  subclass them.
- minor renamings to RegionExtent and its subclasses
- added a bunch of doxygen comments

StoreManager: (static analyzer)
- added 'iterBindings', an iteration method for iterating over the bindings of a
  store. It that takes a callback object (acting like a poor man's closure).
- added 'getRVal' version for store::Binding. Will potentially phase the other
  versions of GetRVal in StoreManager out.
- reimplemented 'getBindings' to be non-virtual and to use 'iterBindings'

BasicStoreManager: (static analyzer)
- implemented 'iterBindings' for BasicStoreManager

llvm-svn: 55688