Part of bug 122:

This change removes the BuildBytecodeInfo flag from the SlotCalculator
class. This flag was needed to distinguish between the Bytecode/Writer
and the AsmWriter. Now that AsmWriter doesn't use SlotCalculator, we can
remove this flag and simplify some code. Also, some minor name changes
to CachedWriter.h needed to be committed (missed in previous commit).

llvm-svn: 13785