Merge branch 'bw/union-merge-refactor'

* bw/union-merge-refactor:
  merge-file: add option to select union merge favor
  merge-file: add option to specify the marker size
  refactor merge flags into xmparam_t
  make union merge an xdl merge favor

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

diff --cc t/t6023-merge-file.sh
Simple merge