Merge branch 'jc/diff-algo-cleanup'

Resurrects the preparatory clean-up patches from another topic that was
discarded, as this would give a saner foundation to build on diff.algo
configuration option series.

* jc/diff-algo-cleanup:
  xdiff: PATIENCE/HISTOGRAM are not independent option bits
  xdiff: remove XDL_PATCH_* macros

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge

diff --cc merge-recursive.c
Simple merge