- patching node inputs fool the register verifier, so fxch, fpop and fpush are now nodes
  without in- and output. They are keeped and hold in the schedule.
- handle all possible constants in sim_Copy()

NEVER return st registers for a floating point node, or the x87 simulator fails

emit block labels for switchjmp targets

 - use of wrong (uninitialized) variable
 - modes was fixed to mode_Iu, but must be the same mode as the other tarval

const are now placed in smallest common dominator block of all it's users
constants have dependency to barrier

made UNKNW, NOREG and vfp registers virtual

made code more firm style :)

added comments (especially for endif)