De-dupe random menu filenames by truncating at first dot, rather than last.

Fix for one of the problems described in issue #380.

bbs.menu("random*"); would display column-width-specific files (e.g.
random.132col.msg) even when they weren't appropriate for the current
user terminal width.

This is fixed by truncating the filenames matching the requested pattern at
their first-dot rather than the last.

The downside is, you can't have a set of random.#.* files, where # is the
unique part of the filename and * is the file-type extension. Just use
the naming pattern "random-#.*" instead (or something similar) instead.