1. Bug fix: was using SLL instead of SLLX for ULongTy. Chump.

2. Handle fp-to-uint conversions directly here instead of relying on
   a pre-transformation to replace them with the 2-step conversion.
3. Use size rather than explicitly checking types when deciding what
   opcodes to use, wherever possible.  This is less error prone (the
   bug fix above was not the first time!).
4. Float-to-pointer casts shd now work though this hasn't been tested.

llvm-svn: 7645