Patch: Don't do unprofitable narrowing of loads.

Our backend only does 32 bit loads. I noticed some loads were narrowed to 8 bits and then had to be reverted back to 32 bit loads. This patch prevents the initial lowering. I've only tested this on my backend. Can someone review and apply this or should I submit a bug?

Index: CodeGen/SelectionDAG/TargetLowering.cpp