i release this patch because my keyboard ("Mitsumi Electric Apple
Extended USB Keyboard" Bus=0003 Vendor=05ac Product=0205 Version=0122)
doesn't have a PrintScr key, so cannot send the right scancode, and
KEY_SYSRQ needs to be modified.

i hope that i've done in the right way ;)
it's tested by me, and it's working, yeah i'm pressing the SAK with F13 :P