Escape filenames

[Todd Larason]

This is similar to Scott's previous "escape spaces in filename" patch
-- if I'd looked here before fixing it myself, I'd have just used
that.

This is a little more comprehensive, though; it should work on any
legal filename now, and patches the new capture_frame method too.

http://groups.google.com/group/rvideo/web/spaces-in-filenames.patch

Still, it seems like there should be a better way. In perl, this
could be handled by using the multi-argument form of open, avoiding
the shell entirely. I can't find an equivalent in ruby, though;
IO.popen appears to be the closest to perl's open pipe magic, but it
doesn't have a shell-avoiding version.