xdiff: change rindex from long to size_t in xdfile_t

rindex describes a index offset which means it's an index into memory
which should use size_t. dstart and dend will be deleted in a future
patch series. Move them to the end to help avoid refactor conflicts.

Signed-off-by: Ezekiel Newren <ezekielnewren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ezekielnewren

xdiff/xtypes.h

@@ -49,7 +49,7 @@ typedef struct s_xdfile {
 	xrecord_t *recs;
 	size_t nrec;
 	bool *changed;
-	long *rindex;
+	size_t *rindex;
 	size_t nreff;
 	ssize_t dstart, dend;
 } xdfile_t;