busybox

hush: implement `type`

Implement support for the POSIX `type` command.  Only POSIX stuff is
supported here, no bash extensions like -p or -P.

In the process, split the $PATH searching code out of builtin_source() and
into its own find_in_path() function so we don't duplicate it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>