Author: Kev <klmitch@mit.edu>

Author: Kev <klmitch@mit.edu>
Log message:

Create a linked list of connections that have queued data.  This allows
flush_connections to scan only the connections that have queued data,
rather than going through every single connection on the server.  This
will improve efficiency, but I doubt it'll have a significant impact on
CPU usage.

Testing:

Compiles and runs with no apparent errors.  It needs to be brute-forced
to make sure there are no assertion failures.

Notes:

If you ever call MsgQClear(), you MUST call client_drop_sendq() as well!
(Perhaps this should be changed to have client_drop_sendq() call
MsgQClear() itself?)

git-svn-id: file:///home/klmitch/undernet-ircu/undernet-ircu-svn/ircu2/trunk@339 c9e4aea6-c8fd-4c43-8297-357d70d61c8c