Fixed a bashism with the use of $RANDOM in hgeditor.
The variable $RANDOM is not POSIX so a portable /bin/sh may not define
it. When creating a directory with a random name it's better to use
mktemp, which, even though is not POSIX, exists in common Unixes
including Linux, OpenBSD, FreeBSD and MacOS X.
% files
dangling -> nothing
% tar
dangling -> nothing
% zip
dangling -> nothing