Merge branch 'kb/p4merge'

Adjust the order mergetools feeds the files to the p4merge backend to match the p4 convention. * kb/p4merge: merge-one-file: force content conflict for "both sides added" case git-merge-one-file: send "ERROR:" messages to stderr git-merge-one-file: style cleanup merge-one-file: remove stale comment mergetools/p4merge: create a base if none available mergetools/p4merge: swap LOCAL and REMOTE