BugFix:

BugFix:
  new_rd_*() functions that call optimize_node() did not
  work if current_ir_graph was not set!
  So, the current_ir_graph is now set and restored.
  Moreover, to speed up the default new_*() and new_d_*()
  cases, new_bd_*() functions have been introduced which use
  current_ir_graph, but not current_block and replace
  the use of _rd_ functions in the comfortable i/f

[r6509]