Add copyrights for all files to comply with the GPL v2.

src/config.h

@@ -1,3 +1,6 @@
+/* Copyright holders: Sarah Walker
+   see COPYING for more details
+*/
 int config_get_int(char *head, char *name, int def);
 char *config_get_string(char *head, char *name, char *def);
 void config_set_int(char *head, char *name, int val);