Add a routine to print "text protocols", and add FTP/HTTP/SMTP/RTSP support.

"Text protocols" are protocols that have the general feel of FTP, with
command lines with a command name and space-separated arguments and
response lines beginning with a 3-digit reply code.  They can also
include HTTP-style headers and an entity body.

We add support for the FTP control channel, HTTP, SMTP, and RTSP.  We
also change the SIP printer to use it.