Lots of small cleanups

- Simplified use_trans_cache() to return at once if is_transactional is set
- Indentation and spelling errors fixed
- Don't call signal_update() if update_binlog_end_pos() is called as the
  function already calls signal_update()
- Removed not used function wait_for_update_bin_log(), which would cause
  errors if ever used.
- Simplified handler::clone() by always allocating 'ref' in ha_open(). To do
  this I added an optional MEM_ROOT argument to ha_open() to be used when
  allocating 'ref'
- Changed arguments to get_system_var() from LEX_CSTRING to LEX_CSTRING*
- Added THD as argument to create_select_for_variable(). Changed also char*
  argument to LEX_CSTRING to avoid strlen() call.
- Change calls to append() to use LEX_CSTRING

mysys/thr_mutex.c

@@ -149,10 +149,11 @@ static inline void remove_from_active_list(safe_mutex_t *mp)
 }
 
 /*
-  We initialise the hashes for deadlock detection lazily.
-  This greatly helps with performance when lots of mutexes are initiased but
+  We initialize the hashes for deadlock detection lazily.
+  This greatly helps with performance when lots of mutexes are initialized but
   only a few of them are actually used (eg. InnoDB).
 */
+
 static int safe_mutex_lazy_init_deadlock_detection(safe_mutex_t *mp)
 {
   if (!my_multi_malloc(MY_FAE | MY_WME,