Make IRC_WHO also search username/servername/hostname.

Make IRC_WHO also search username/servername/hostname.

Dana Dahlstrom reported that IRC_WHO did not follow
RFC 2812, Section 3.6.1. Specifically:

- IRC_WHO did not send "G" flag instead if "H" if client was away
- did not search username/servername/hostname etc. if argument
  was not a channel.

Fix all of the above and tidy things up a bit.
Also add IRC_WHO test script contributed by Dana.