Merge branch 'jt/diff-color-move-fix' into next

A handful of bugfixes and an improvement to "diff --color-moved".

* jt/diff-color-move-fix:
diff: define block by number of alphanumeric chars
diff: respect MIN_BLOCK_LENGTH for last block
diff: avoid redundantly clearing a flag

diff --cc Documentation/diff-options.txt
Simple merge

diff --cc diff.c
Simple merge