due to the many external programs that come to plan9 nowadays i've added a 'man' target for installing external man pages located in the same directory as the source. the command is common to the 'mkone' and 'mkmany' include files and works simply by:

- the source code writer creates one or several man pages named '$TARG.man'
- the source code writer defines MAN= in the mkfiles for their code, $MAN points to the section the man pages are destined for (i.e. /sys/man/1/ for section 1, commands)
- the user types 'mk man' or 'mk somefile.man' to have the man page installed.

for now, the 'man' target is not included in 'mk all'...