MFC r258269: Refactor draw-beastie function.

Discussed on:	-hackers
MFC r258270:

Add a try-include word (which acts the same as "include") and use it to
conditionally include (but ignore failures) /boot/loader.rc.local and
/boot/menu.rc.local -- to make customizing the menu easier.

Reviewed by:	alfred
Discussed on:	-hackers