fix bug causing "<invalid>" instructions in traces on 64-bit systems

* ChangeLog:
2013-04-10  Peter Gavin  <pgavin@gmail.com>

	* cpu/or32/or32.c: (insn_extract) make sure the new extracted bit
	is unsigned, otherwise the result may become negative and will be
	sign-extended when cast to a 64-bit integer.  This fixes the bug
	on 64-bit systems where "<invalid>" would be printed in traces for
	valid instructions