Optionally generate verbose parent links

The new option 'enable-subject-links' must be used to enable the verbose
parent-links in commit view.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -73,6 +73,7 @@ struct cgit_repo {
 	int enable_log_filecount;
 	int enable_log_linecount;
 	int enable_remote_branches;
+	int enable_subject_links;
 	int max_stats;
 	time_t mtime;
 	struct cgit_filter *about_filter;
@@ -181,6 +182,7 @@ struct cgit_config {
 	int enable_log_filecount;
 	int enable_log_linecount;
 	int enable_remote_branches;
+	int enable_subject_links;
 	int enable_tree_linenumbers;
 	int local_time;
 	int max_repo_count;