Rather than duplicating the documentation for the various "gc" options
let's include the "gc" docs from git-config. They were mostly better
already, and now we don't have the same docs in two places with subtly
different wording.
In the cases where the git-gc(1) docs were saying something the "gc"
docs in git-config(1) didn't cover move the relevant section over to
the git-config(1) docs.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
