Earlier show-branch gave names only to commits reachable via first
parent ancestry chain.  Change the naming code to name everybody.

The original idea was to stop at the first merge point in the
topological order, and --more=<n> to show commits until we show <n>
more extra merge points.  However depending on the order of how we
discover the commits, it additionally showed parents of the <n>th
merge points, which was unnecessary.
Signed-off-by: NJunio C Hamano <junkio@cox.net>