Copy channel name from command on lowerTS JOIN/SJOIN, this makes the capitalization of the channel name timestamped like modes are.
Another handling of SJOINs without nicks: Propagate them if the channel is +P or the channel already existed, otherwise remove the channel again and do not propagate the SJOIN.
+ branches/release-2.1 -> 2.2 base + 3.0 -> branches/cxxconversion + backport some immediate 3.0 functionality for 2.2 + other stuff
