Merge branch 'jc/merge'

"git merge FETCH_HEAD" learned that the previous "git fetch" could be to create an Octopus merge, i.e. recording multiple branches that are not marked as "not-for-merge"; this allows us to lose an old style invocation "git merge <msg> HEAD $commits..." in the implementation of "git pull" script; the old style syntax can now be deprecated. * jc/merge: merge: deprecate 'git merge <message> HEAD <commit>' syntax merge: handle FETCH_HEAD internally merge: decide if we auto-generate the message early in collect_parents() merge: make collect_parents() auto-generate the merge message merge: extract prepare_merge_message() logic out merge: narrow scope of merge_names merge: split reduce_parents() out of collect_parents() merge: clarify collect_parents() logic merge: small leakfix and code simplification merge: do not check argc to determine number of remote heads merge: clarify "pulling into void" special case t5520: test pulling an octopus into an unborn branch t5520: style fixes merge: simplify code flow merge: test the top-level merge driver