Merge branch 'jk/diff-compact-heuristic'

Patch output from "git diff" and friends has been tweaked to be
more readable by using a blank line as a strong hint that the
contents before and after it belong to a logically separate unit.

* jk/diff-compact-heuristic:
diff: undocument the compaction heuristic knobs for experimentation
xdiff: implement empty line chunk heuristic
xdiff: add recs_match helper function

diff --cc diff.c
Simple merge

diff --cc xdiff/xdiff.h
index 4fb7e79410c22fba1fb390af2e09008e932f5ea8,d1dbb2750acb9da8f6e61d71ce4e51e689e6ae88..7423f77fc8b2682c121e8d4adb855337e107b29e
--- 1/xdiff/xdiff.h
--- 2/xdiff/xdiff.h
+++ b/xdiff/xdiff.h
@@@ -41,7 -41,10 +41,9 @@@ extern "C" 
  
  #define XDF_IGNORE_BLANK_LINES (1 << 7)
  
+ #define XDF_COMPACTION_HEURISTIC (1 << 8)
+ 
  #define XDL_EMIT_FUNCNAMES (1 << 0)
 -#define XDL_EMIT_COMMON (1 << 1)
  #define XDL_EMIT_FUNCCONTEXT (1 << 2)
  
  #define XDL_MMB_READONLY (1 << 0)