I made a mistake in not hosting this script from an hg repository; it’s already changed a few times since I originally posted. So, I fixed that. Now one can
hg clone http://hg.mozilla.org/users/cjones_mozilla.com/tryselect cd $repo ../tryselect/tryselect
Permissions and so forth should be set correctly. (Protip: I symlinked tryselect/tryselect into a directory in my $PATH.)
If you find bugs, please fix them!