update.sh: tame the wild show_progress=1 beast

update.sh: tame the wild show_progress=1 beast

Since we've switched from "git remote update" to "git fetch --multiple"
we are now passing along the "--progress" option when requested
($show_progress) and Git supports it (v1.7.1+).

This is a good thing as we can now finally get decent fetch progress.

However, there's no way to tell "git fetch" to give us all the
progress, but please do not shower us in a storm of endless bits
of unwanted, exploded ref update spam messages.

One might think that "git fetch --quiet --progress" would do the
trick.  One would be wrong about that.

If $show_progress is set to 2 or greater continue to provide the
totally unrefreshing spam shower.

However, if $show_progress is only set to 1, use a "git fetch"
wrapper that knows how to pass through the nice progress bits we
want to see while condensing the shower to just one drop per remote
(usually there's only one remote) that gives a ref activity summary.

Obviously, if $show_progress is unset, set to "" or set to "0" we
do not pass "--progress" at all, so there's no issue in that case.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>