Add max-commit-count parameter to cgitrc

This enabled customizing number of commits shown per page in log view. It
also changes the default from 100 to 50, mainly due to the more cpu
intensive log pages (number of files/lines changed) but also since 100
log messages requires excessive scrolling.

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

cgit.h

@@ -87,6 +87,7 @@ extern int cgit_cache_static_ttl;
 extern int cgit_cache_max_create_time;
 
 extern int cgit_max_msg_len;
+extern int cgit_max_commit_count;
 
 extern char *cgit_repo_name;
 extern char *cgit_repo_desc;