Merge branch 'jc/diff-algo-attribute'

The "diff" drivers specified by the "diff" attribute attached to
paths can now specify which algorithm (e.g. histogram) to use.

* jc/diff-algo-attribute:
  diff: teach diff to read algorithm from diff driver
  diff: consolidate diff algorithm option parsing

diff --cc Documentation/gitattributes.txt
Simple merge

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge

diff --cc userdiff.c
Simple merge