Make the filename syntax more palatable.

Make the filename syntax more palatable.

Quotes are needed for talking about too many interesting files.  In
particular, it's nice to be able to refer to, say, /tmp/.X11-unix/X0
from the command-line without quotes.

This change introduces a new function conf_fname which extends the word
characters appropriately during a read, and makes the various clients --
file, un, and exec -- actually use it rather than calling conf_name
directly.