Fix a major source of "type unsafety", where a cast is neccesary, but can

Fix a major source of "type unsafety", where a cast is neccesary, but can
be put either before or after a load.  We chose to cast the value loaded
instead of the pointer to load from.

Fixes bug: test/Regression/Transforms/LevelRaise/2002-05-10-LoadPeephole.ll

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2621 91177308-0d34-0410-b5e6-96231b3b80d8