be: Do not consider should_be_same in reg_req_has_constraint().
be: Do not consider should_be_same in reg_req_has_constraint().

This is not a hard constraint like the others and does not break the register allocation, if a Perm is pushed across the node with should_be_same.
This restores the behavior before the register constraint reorganization and removes lots of xchgs in the testsuite again.

jonashaag/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,davidgiven/libfirm,jonashaag/libfirm,libfirm/libfirm,davidgiven/libfirm,MatzeB/libfirm,libfirm/libfirm,davidgiven/libfirm,8l/libfirm,killbug2004/libfirm,killbug2004/libfirm,8l/libfirm,jonashaag/libfirm,jonashaag/libfirm,killbug2004/libfirm,libfirm/libfirm,davidgiven/libfirm,killbug2004/libfirm,8l/libfirm,davidgiven/libfirm,jonashaag/libfirm,MatzeB/libfirm,davidgiven/libfirm,killbug2004/libfirm,MatzeB/libfirm,killbug2004/libfirm,jonashaag/libfirm,8l/libfirm,MatzeB/libfirm,jonashaag/libfirm,killbug2004/libfirm,8l/libfirm,davidgiven/libfirm,libfirm/libfirm,8l/libfirm,8l/libfirm