Adding the initial implementation of the SlotTable class. This class is

the Abstract Data Type that holds slot number values and associates them
with Type* and Value*. The SlotTable is simply the holder of the slot
numbers and provides a controlled interface for building the table. It does
not enforce any particular idiom or functionality for manipulating the slot
numbers.

This is part of bug_122. The SlotCalculator and SlotMachine classes will
follow.

llvm-svn: 13764