bug#1283: 23.0.60; minibuffer-complete and file names with `-' or `_'

[Stephen Berman]

In GNU Emacs 23.0.60.12 (i686-pc-linux-gnu, GTK+ Version 2.12.9)
 of 2008-10-25 on escher

On my system, /lib contains these two files:

   libthread_db-1.0.so
   libthread_db.so.1

When I type `C-x d' or `C-x C-f' and then `/lib/libthr TAB', the path is
completed to `/lib/libthread_db.so.1'.  

Also on my system, /usr/lib contains these three files:

   libthread_db.so
   libthreadweaver.so.4
   libthreadweaver.so.4.1.0

When I type `C-x d' or `C-x C-f' and then `/usr/lib/libthr TAB', the
path is completed to `/usr/lib/libthreadweaver.so.4'.  A second TAB
tells me this is complete but not unique and the *Completions* buffer
shows me (only) libthreadweaver.so.4 and libthreadweaver.so.4.1.0.

This is with -Q, and I get the same behavior with completion-styles set
to any of `basic', `emacs21', emacs22', or `partial-completion'.