VERY overdue .gitignore

 Due to the nature of live-build, *thousands* of untracked files build up over
 time, since live-build makes a complete Debian system in chroot/ (and makes
 many other files in cache/ and binary/). Finally git status -u won't take 10
 seconds on a working repository.
clean out a backup file

 How this lasted so long I don't know...
use host triplets properly in cmake packages
stupid libpng revved again