Add missing exit_cond() to lock_global_read_lock().

Docs/manual.texi:
  Recommend gdb 5.1
sql/lock.cc:
  Add missing exit_cond when waiting to lock_global_read_lock()
sql/sql_select.cc:
  Cleanup

Docs/manual.texi

@@ -7814,7 +7814,7 @@ Some known problems when running MySQL on Linux-Alpha:
 @itemize @bullet
 @item
 Debugging threaded applications like MySQL will not work with
-@code{gdb 4.18}.  You should download and use gdb 5.0 instead!
+@code{gdb 4.18}.  You should download and use gdb 5.1 instead!
 
 @item
 If you try linking @code{mysqld} statically when using @code{gcc}, the
@@ -52064,7 +52064,9 @@ more information if @code{mysqld} crashes.
 
 With some older @code{gdb} versions on Linux you must use @code{run
 --one-thread} if you want to be able to debug @code{mysqld} threads.  In
-this case you can only have one thread active at a time.
+this case you can only have one thread active at a time.  We recommend you
+to upgrade to gdb 5.1 ASAP as thread debugging works much better with this
+version!
 
 When running @code{mysqld} under gdb, you should disable the stack trace
 with @code{--skip-stack-trace} to be able to catch segfaults within gdb.

sql/lock.cc

@@ -543,6 +543,7 @@ bool lock_global_read_lock(THD *thd)
     while (protect_against_global_read_lock && !thd->killed)
       pthread_cond_wait(&COND_refresh, &LOCK_open);
     waiting_for_read_lock--;
+    thd->exit_cond(old_message);
     if (thd->killed)
     {
       (void) pthread_mutex_unlock(&LOCK_open);

sql/sql_select.cc

@@ -4116,22 +4116,16 @@ do_select(JOIN *join,List<Item> *fields,TABLE *table,Procedure *procedure)
     if (error == -3)
       error=0;					/* select_limit used */
   }
-  if (!table)					/* If sending data to client */
-  {
   if (error < 0)
     join->result->send_error(0,NullS);	/* purecov: inspected */
   else
+  {
+    if (!table)				// If sending data to client
     {
       join_free(join);				// Unlock all cursors
       if (join->result->send_eof())
 	error= -1;
     }
-  }
-  else if (error < 0)
-    join->result->send_error(0,NullS); /* purecov: inspected */
-
-  if (error >= 0)
-  {
     DBUG_PRINT("info",("%ld records output",join->send_records));
   }
   if (table)
@@ -4226,10 +4220,8 @@ sub_select(JOIN *join,JOIN_TAB *join_tab,bool end_of_records)
 	  info->file->unlock_row();
       }
     } while (!(error=info->read_record(info)));
-    if (error > 0)				// Fatal error
-      return -1;
   }
-  else if (error > 0)
+  if (error > 0)				// Fatal error
     return -1;
 
   if (!found && on_expr)