Merge branch 'js/merge'

Merge branch 'js/merge'

* js/merge:
  merge-recursive: add/add really is modify/modify with an empty base
  Get rid of the dependency on RCS' merge program
  merge-file: support -p and -q; fix compile warnings
  Add builtin merge-file, a minimal replacement for RCS merge
  xdl_merge(): fix and simplify conflict handling
  xdl_merge(): fix thinko
  xdl_merge(): fix an off-by-one bug
  merge-recursive: use xdl_merge().
  xmerge: make return value from xdl_merge() more usable.
  xdiff: add xdl_merge()