obslog: correct help to state that obslog is the command name
hg help obslog says the following, which is a bit confusing:
hg olog [OPTION]... [[-r] REV]... aliases: olog
Since the primary command name is determined by the order the commands are
defined in, and we use 'obslog' as the name for the pager, I've chosen
hg obslog as the canonical name and am only adjusting the help string.