The old GRUB menu builder script is quite slow, typically taking
several seconds. This is a real annoyance since it's run every time
you switch to a new configuration. Therefore this patch replaces the
Bash script with a much faster Perl script. In a VirtualBox test, the
execution time went from 2.7s to 0.1s. The Perl version is also more
correct because it uses XML to get the GRUB configuration (through
builtins.toXML), so there are no shell escaping issues.
The new script currently lacks support for subconfigurations defined
through "nesting.children".
