Merge branch 'jk/merge-file-exit-code' into maint

"git merge-file" tried to signal how many conflicts it found, which
obviously would not work well when there are too many of them.

* jk/merge-file-exit-code:
  merge-file: clamp exit code to maximum 127

diff --cc builtin/merge-file.c
Simple merge

diff --cc t/t7600-merge.sh
Simple merge