Merge branch 'jk/fsck-doc'

"git fsck --connectivity-only" omits computation necessary to sift the objects that are not reachable from any of the refs into unreachable and dangling. This is now enabled when dangling objects are requested (which is done by default, but can be overridden with the "--no-dangling" option). * jk/fsck-doc: fsck: always compute USED flags for unreachable objects doc/fsck: clarify --connectivity-only behavior