Merge branch 'jk/xdiff-interface'

The interface into "xdiff" library used to discover the offset and
size of a generated patch hunk by first formatting it into the
textual hunk header "@@ -n,m +k,l @@" and then parsing the numbers
out.  A new interface has been introduced to allow callers a more
direct access to them.

* jk/xdiff-interface:
  xdiff-interface: drop parse_hunk_header()
  range-diff: use a hunk callback
  diff: convert --check to use a hunk callback
  combine-diff: use an xdiff hunk callback
  diff: use hunk callback for word-diff
  diff: discard hunk headers for patch-ids earlier
  diff: avoid generating unused hunk header lines
  xdiff-interface: provide a separate consume callback for hunks
  xdiff: provide a separate emit callback for hunks

builtin/merge-tree.c

@@ -110,7 +110,8 @@ static void show_diff(struct merge_list *entry)
 	xpp.flags = 0;
 	memset(&xecfg, 0, sizeof(xecfg));
 	xecfg.ctxlen = 3;
-	ecb.outf = show_outf;
+	ecb.out_hunk = NULL;
+	ecb.out_line = show_outf;
 	ecb.priv = NULL;
 
 	src.ptr = origin(entry, &size);