Related to bug #217, added command 'fail accept <errno>' to debug client's commands.

Reproduce #217 by connecting with telnet to debug client interface and execute command:

fail accept 23

and try to execute read query, for example, with

mysql -h 127.0.0.1 -P 4008 -u maxuser -pmaxpwd -e 'select current_user(), @@server_id'

server/include/dcb.h

@@ -190,6 +190,8 @@ unsigned char dcb_fake_write_errno[1024];
 __int32_t     dcb_fake_write_ev[1024];
 bool          fail_next_backend_fd;
 bool          fail_next_client_fd;
+bool          fail_next_accept;
+int           fail_accept_errno;
 #endif
 
 /* A few useful macros */