DESCRIPTION:
When mysqld is started in Named Pipe mode with a pipe name
which is already in used by another instance, neither of the
instances are able to shutdown properly when a shutdown command
is received from a TCP socket in any of the processes .
mysqld.exe is not therefore not terminated.

ANALYSIS :
When a MySQL client sends a shutdown command using a TCP socket
to a server which also happens to be using named Pipes shared by 
another instance. kill_server() and close_connections() are called
on the correct instance identified by the TCP socket. However the 
worker thread servicing the named pipe connection is terminated on 
the instance first launched in chronological order, which might not 
be the same instance. This results in handle_connections_methods() 
waiting indefinitely on COND_handler_count and the main thread 
never exits.

FIX :
Code has been added to make sure the Named Pipe specified is
not already in use. If it is so an error is shown and the process is
aborted.