PLP now supports %-escapes in printcap filter entries. Eg., a printcap
entry containing this...

	:if=/usr/lib/plp/ascii2ps -f %h -u %u %a:

would mean that something like the following command would be used as
the filter:

	/usr/lib/plp/ascii2ps -f 'hostname' -u 'jrandom' 'acct'

which saves verbosity and is easier to understand. Here's the list of
%-escapes currently implemented:

    %p  what the user invoked printer as (-P option)
    %P  the canonical name for this printer (for accounting)

    %a  accounting file (af printcap entry)
    %s  printer status file (ps printcap entry)
    %w  page width in columns (pw printcap entry, lpr -w option)
    %l  page length in lines (pl printcap entry)
    %x  page width in pixels (px printcap entry)
    %y  page height in pixels (py printcap entry)
    %m  cost per 1000 pages (co printcap entry)

    %i  indent (lpr -i option)
    %n  username
    %h  hostname
    %N  filename
    %R  accounting name (from lpr)
    %J  job name
    %C  class name (priority)
    %F  job format (old BSD style)
    %Z  Z-options

    %S  printer comment (cm printcap entry)
    %Y  line of perms file where match took place
    %c  "-c" if job format is literal (l)

