Use symbolic constants for diff-raw status indicators.

Both Cogito and StGIT prefer to see 'A' for new files.  The
current 'N' is visually harder to distinguish from 'M', which is
used for modified files.  Prepare the internals to use symbolic
constants to make the change easier.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.h

@@ -82,4 +82,20 @@ extern int diff_queue_is_empty(void);
 
 extern void diff_flush(int output_style, int line_terminator);
 
+/* diff-raw status letters */
+#define DIFF_STATUS_ADDED		'N'
+#define DIFF_STATUS_COPIED		'C'
+#define DIFF_STATUS_DELETED		'D'
+#define DIFF_STATUS_MODIFIED		'M'
+#define DIFF_STATUS_RENAMED		'R'
+#define DIFF_STATUS_TYPE_CHANGED	'T'
+#define DIFF_STATUS_UNKNOWN		'X'
+#define DIFF_STATUS_UNMERGED		'U'
+
+/* these are not diff-raw status letters proper, but used by
+ * diffcore-filter insn to specify additional restrictions.
+ */
+#define DIFF_STATUS_FILTER_AON		'A'
+#define DIFF_STATUS_FILTER_BROKEN	'B'
+
 #endif /* DIFF_H */