Minor improvements and clean up

removed references to master_fd and slave_fd
defined macro ioctl_FIONBIO to replace calls to ioctl
removed codes previously obsoleted by the introduction of hostgroups
created a global variable (glo_mysql_thrarr) to keep track of mysql threads
function reconnect_server_on_shut_fd() is now aware of hostgroups
removed fds from main()
removed any reference to thread dump_timers()
conn_poll() doesn't return an int
sync_net() is now a private function
added private function queue_back_client_pkt()
Introduced activate_backend_for_hostgroup() that should deprecate active_backend_for_hostgroup
Removed a lot of warnings when compiled with -Wall
introduced struct _mysql_server_hostgroup_entry_t , but not used yet
Minor improvement
Several improvement and bug fixes

Removed "mysql_server *server_ptr" from server_ptr, replaced by "MSHGE *ms"
mysql_data_stream_t now has a pointer to its mysql_backend if this is a server (NULL for clients)
bytes sent/recv to/from each backends are now counted
pkts sent/recv to/from each backend are now counted
table runtime_hostgroups provides further details
Fixed issue #16