Hello. Here is an implementation of bash-like "test" command. Many file
tests are omitted because they are useless in grub (e.g. -c test). I
also added 3 extension: lexicographical comparing, prefixed -gt and -lt
(it skips common prefix. Useful for comparing versions. e.g. [ vmlinuz-3
-plt vmlinuz-11 ] is true) and biased -nt/-ot which adds s specified
amount of seconds to mtime.