Merge branch 'js/close-packs-before-gc'

Many codepaths that run "gc --auto" before exiting kept packfiles mapped and left the file descriptors to them open, which was not friendly to systems that cannot remove files that are open. They now close the packs before doing so. * js/close-packs-before-gc: receive-pack: release pack files before garbage-collecting merge: release pack files before garbage-collecting am: release pack files before garbage-collecting fetch: release pack files before garbage-collecting