GitLab

 - Use a new example, that has a lan in it
   - including an updated picture and an updated expt report email msg.
 - Update the loop example to make a LAN, since it is non-obvious, and
   very handy.
 - Make LANs in general more obvious.
 - Make Netbuild more obvious.
 - Update our "current images" to FBSD47 and RHL73.
 - Change "the Testbed" to "Emulab" everywhere...
 - Make the difference between control net and exptl. net more obvious,
   and add links to the faq questions in a couple of places.
 - In the part that talks about getting help, remind them to keep tbops on
   each message.

There's still a lot more to be done with the docs, but this is a start, at
least.

Also went over references to FreeBSD 4.0 and RedHat 6.2, and changed them
to 4.3 and 7.1 as appropriate