git log mtime, switch to turn off mtime checking

check mtime using git log if available
add switch to disable mtime checking
lsof -Q to not fail on empty result
update gitignore
kill processes holding open files in overlayfs

gnome-keyring-daemon is started by pam on login, opening files in the
mounted overlayfs. kill all processes which still have open files there
after the build is complete.
fix content disposition, again
fix documentation generation
buildslack v0.1.6
install man pages
content-disposition, aka i hate the web
add switch to continue upgrades after failed build
remove duplicates from update queue

duplicates inserted due to mtime detection are now removed
umount overlay recursively
fix typo breaking mtime detection

i really need to write tests for this stuff :)
hook up backup toggle
better setup notes
gitignore buildslack.kit