Optimize binder.
Optimize binder.

	* src/binder/binder.cc: Break out of the loops when an already-bound
	variable is encountered, instead of performing no-op loops up to the
	toplevel.

aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi