Bug fix with post scripts

[elikaski]

Compiling a simple Hello World program generates assembly code that contains:

	# (external call)
	movl (sp), %esp  # <REQ>
	movl $printf, (external)

When using post/xor.py (and other post scripts), the corresponding instructions generated are:

	# (external call)
	#xor> movl (sp), %esp  # <REQ>
	xorl %ebx, %ebx
	xorl (sp), %ebx
	xorl %esp  # <REQ>, %ebx
	xorl %ebx, %esp  # <REQ>

The third instruction is the problematic: xorl %esp # <REQ>, %ebx

The root cause is that the comment (# <REQ>) is also being identified as the "destination" register My change makes it discard the comment