Here comes a nasty patch, although I am not ready to push it yet. I will

first pull, merge,test, and get it to work.

The main change is the new replication code - now we have two slave threads
SQL thread and I/O thread. I have also re-written a lot of the code to 
prepare for multi-master implementation. 

I also documented IO_CACHE quite extensively and to some extend, THD class.

sql/sql_lex.h

@@ -94,7 +94,6 @@ typedef struct st_lex_master_info
 {
   char* host, *user, *password,*log_file_name;
   uint port, connect_retry;
-  ulong last_log_seq;
   ulonglong pos;
   ulong server_id;
 } LEX_MASTER_INFO;