Commit all changes prior to addressing the x86 spilling situation in
the register allocator.

-- Fix nonsensical x86 addressing mode hacks in mangleIndexTree
   and getAmode.

-- Make char-sized loads work properly, using MOVZBL.

-- In assignIntCode, use primRep on the assign node to determine
   the size of data transfer, not the size of the source.

-- Redo Integer primitives to be in line with current representation
   of Integers.