Merge branch 'jc/index-pack-fsck-levels'

The "--fsck-objects" option of "git index-pack" now can take the optional parameter to tweak severity of different fsck errors. * jc/index-pack-fsck-levels: index-pack: --fsck-objects to take an optional argument for fsck msgs index-pack: test and document --strict=<msg-id>=<severity>...