"git apply --3way" learned to honor merge.conflictStyle
configuration variable, like merges would.

* dl/apply-3way-diff3:
  apply: respect merge.conflictStyle in --3way
  t4108: demonstrate bug in apply
  t4108: use `test_config` instead of `git config`
  t4108: remove git command upstream of pipe
  t4108: replace create_file with test_write_lines