of pty/tty based (since they have several annoying problems
associated). Note that permission is granted via the use of an "acl"
file; /dev/tip/machine.acl, which must be set to the group of the
project the node is in, so the user can read out the process id number
and the random bits that are used by capture to grant permission to
use (tip sends the random bits across first thing). This handshake is
due to change to a request/challenge scheme as described by Dave in
email to the testbed list.

Standardized error message format

mode correct.  It works now.  Really.

Set non-blocking write the correct way this time!

2. Add pty flush and revoke on a shutdown (USR2) signal
3. cleanups

code I found in /foo/x/mike/src/capture/capture.c. Second, add a -r
option to open up a second log file called the "run" file, which is
intended to be used for the experiment session log. This log is
restarted with a SIGUSR1. Third, add SIGUSR2 handler to close the
pty side of the capture, which has the nice side effect of causing tip
to exit gracefully.

Note that this has a hardcoded value for NBPG, a define that's only
present in the digiboard headers.  In the interest of minimal source
code changes (heh, heh, heh) I left it alone. :p

Works on *bsd, and now Linux.  Manpage included at no charge,
though if someone wants to figure out why the manpage only
works under BSD ("Because Dave is an idiot" is not an acceptable
answer, true as it may be), that'd be cool.