[CFR] Mergemaster auto upgrade patch

I've thrown together a quick mergemaster enhancement (under a new 
command line switch: -U) that will automatically upgrade files that have 
changed in the /usr/src/etc distribution but the user hasn't changed. 
Great applications are for when you trust that the project isn't going 
to break everything and only don't want mergemaster to squash files that 
you have customized.

Patch location: 
http://people.freebsd.org/~gordon/patches/mergemaster.mtree.diff

Please try it out!

Thanks,
Gordon