Debug: Only print queued lines if they are really just queued

Previously, every line that was forwarded to the IRCd was printed twice in debug
mode. Once when it got added to the send queue and a second time when it was
actually sent. However, most of the time this queue is empty and thus the two
events happened at approximately the same time.

Thus, this patch now changes the debug output. Lines are only printed extra if
they really have to wait in the queue for a while before they can be sent out.

This has the positive effect of making the debug output more readable, because
it is shorter and less repetitive and it makes it more obvious when znc actively
throttles the traffic that is sent out.

Signed-off-by: Uli Schlachter <psychon@znc.in>
make clean: Only delete files that can be regenerated

Previously, "make clean" would happily delete swig's output files even though
configure did not find swig and thus these files could not be generated again.

This half-fixes issue 276. It would be great if the Makefiles never delete files
which are part of the tarball, but at least they now don't delete files which
cannot be regenerated.

Signed-off-by: Uli Schlachter <psychon@znc.in>
Makefile: Remove unused (and broken) variable

Signed-off-by: Uli Schlachter <psychon@znc.in>