breaking the crunchgen logic into a share/mk file

[Adrian Chadd]

Hi,

I've broken out the crunchgen logic from src/rescue/rescue into a
share/mk file - that way it can be reused in other areas.

The diff is here: http://people.freebsd.org/~adrian/crunchgen-mk.diff

This bsd.crunchgen.mk file is generic enough to use in my
busybox-style thing as well as for src/rescue/rescue/.

Comments, feedback, etc welcome!


Adrian