Users that create Planetlab experiments will now get email coming back via
the emulabman@emulab.net alias.  The technique is simple:  stash away the
experiment head uid in a file corresponding to the slice's name over in
ops:/etc/mail/plab-slice-addrs.  The silly procmail config file I've committed
here reads this file (if it exists) and forwards mail to the user's email addr
contained therein if the incoming message contains the name of their slice.
There is no install target for this procmail filter;
I hand installed it and hooked it in.