Allow pointers to pointers in logical addressing mode.

Allow pointers to pointers in logical addressing mode.

A few optimizations are updates to handle code that is suppose to be
using the logical addressing mode, but still has variables that contain
pointers as long as the pointer are to opaque objects.  This is called
"relaxed logical addressing".

|Instruction::GetBaseAddress| will check that pointers that are use meet
the relaxed logical addressing rules.  Optimization that now handle
relaxed logical addressing instead of logical addressing are:

 - aggressive dead-code elimination
 - local access chain convert
 - local store elimination passes.