Disallow access to Makefile's in the www tree.

Cherry-picked from 9e74608a1fe0.
Fix "language" typo.

Cherry-picked from f3d1cf346404.
Add note that maintainer-* make targets replace normal ones and
put maintainer documentation in more natural order.

Cherry-picked from: ffe9860e41, a02a0ddb9.
Suppress notice of undefined index.

Cherry-picked from 443d2a349735.
Improve error message when running processes found.

Cherry-picked from e1dc6c4ffb.
Fix HTML validator error.

Cherry-picked from 919713e3ec.
Don't remove chroot mountpoints after unmounting.

The 'rmdir' gave spurious warning messages "Device or resource busy"
while fuser/lsof incidated no open files. This only occurred when
running multiple judgedaemons on one machine, see also:
https://www.a-eskwadraat.nl/archive/domjudge-devel/2013-July/001284.html

Cherry-picked from 452a5e75a4.
Bugfix: properly close unused resources (found by Coverity scan).

Cherry-picked from 2d2472ce9bcd.
Update ChangeLog.
Rename SQL upgrade scripts to latest releases.