Save a pointer to the event_alloc parameter in the plugin open function.

That way we don't need to pass event_alloc around to the log client
functions.

plugins/sudoers/sudoers.h

@@ -428,6 +428,7 @@ extern uid_t timestamp_uid;
 extern gid_t timestamp_gid;
 extern sudo_conv_t sudo_conv;
 extern sudo_printf_t sudo_printf;
+extern struct sudo_plugin_event * (*plugin_event_alloc)(void);
 
 /* sudoers_debug.c */
 bool sudoers_debug_parse_flags(struct sudo_conf_debug_file_list *debug_files, const char *entry);