log and rev-list: add --graph option

This new option causes a text-based representation of the history to be
printed to the left of the normal output.

Signed-off-by: Adam Simpkins <adam@adamsimpkins.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.h

@@ -66,7 +66,8 @@ struct rev_info {
 	/* Format info */
 	unsigned int	shown_one:1,
 			abbrev_commit:1,
-			use_terminator:1;
+			use_terminator:1,
+			missing_newline:1;
 	enum date_mode date_mode;
 
 	const char **ignore_packed; /* pretend objects in these are unpacked */
@@ -89,6 +90,9 @@ struct rev_info {
 	/* Filter by commit log message */
 	struct grep_opt	*grep_filter;
 
+	/* Display history graph */
+	struct git_graph *graph;
+
 	/* special limits */
 	int skip_count;
 	int max_count;