- Use a default node compare attribute function for all nodes, except the ones

- Use a default node compare attribute function for all nodes, except the ones
  where CSE is explicitely forbidden. This fixes some bugs where a cmp
  function was missing.
- Don't make all the nodes mode_T by default. They keep their normal mode
  node and only get set to mode_T is we actually use am_Dest
- get rid of src_mode and tgt_mode node attribute, you can get the modes
  by looking at the conv output mode and the arguments mode. This fixes
  some bugs where the src_mode and tgt_mode attributes were wrong
- cleaned up and fixed some bugs in addressmode optimisation