removepreview.sh, snapmergepuppy, rc.shutdown fixes

Shinobar improved script /usr/local/petget/removepreview.sh, for case of a file getting exposed in a lower Aufs/Unionfs layer when removed from the top. I have applied some of it into Woof.

Rerwin sent me a pm about some further changes to /usr/sbin/snapmergepuppy. I have applied rerwin's suggestion to screen out /.XLOADED so that it doesn't end up on the Flash drive save-file. I am leaving out rerwin's suggestion to screen out /dev/snd, as I want snapmergepuppy to mimic the behaviour of normal saves (on hard drive, that do not use snapmergepuppy), in which all of /dev is currently "saved". This is pending a review of the whole save of /dev concept.

Karl Godt posted some more fixes to /etc/rc.d/rc.shutdown, regarding to killing of stray processes and zombies. Applied.
I got this from: http://www.murga-linux.com/puppy/viewtopic.php?t=73122

Woof commit:
http://bkhome.org/fossil/woof2.cgi/info/a94d3c19f4

Tags: woof