- use mode_Iu for all nodes producing integer values (because registers are mode_Iu), this gives more possibilities for cse
- use mode_D for all nodes producing float values, this gives more possibilities for cse
- Introduce NoReg and Unknown nodes so we don't have strange projs from the start barrier
- Rewrite transform phase:
  - while transforming we now build a completely new graph on a new irg (while looking at the old graph)
  - no need to transform constants in advance anymore
  - several smaller fixes+cleanups

- calculate execfreqs after the transform phase
- set irg phase state to phase_backend
- do more verification after the transform phase

don't make ignore registers automatically callee-save, don't use mach_mode for constants if it is a reference mode

dump_compound_init(): can handle initialiezer bigger than the type size (last compound field is an array)
more doxygen docu added