* Bug fixes:

  - Fix problems where the constant table would not get updated when
    resolving constants causes other constants to change.

Changes to the V2 bytecode format
  - Null values are implicitly encoded instead of explicitly, this makes
    things more compact!
  - More compactly represent ConstantPointerRefs
  - Bytecode files are represented as:
      Header|GlobalTypes|GlobalVars/Function Protos|Constants|Functions|SymTab
    instead of
      Header|GlobalTypes|Constants|GlobalVars/Function Protos|Functions|SymTab
    which makes a lot of things simpler.

Changes to the reader:
  - Function loading code is much simpler.  We now no longer make function
    PlaceHolderHelper objects to be replaced with real functions.

llvm-svn: 5748