cvsimport - cleanup of the multi-indexes handling

cvsimport - cleanup of the multi-indexes handling

Indexes are only needed when we are about preparing to commit. Prime them
inside commit() when we have all the info we need, and remove all the
redundant index setups.

While we are at it, make sure that index handling is correct when opening
new branches, and on initial import.

Signed-off-by: Martin Langhoff <martin@catalyst.net.nz>
Signed-off-by: Junio C Hamano <junkio@cox.net>