Synopsis:
   $winserv([<window>])

Technical:
   This function returns the index to the current server for the specified
   window number or name.  If no window is specified, the current is assumed.

Practical:
   This function is a convenient way for a script to know what the current
   server is.  It returns the index in the server list, which can then in
   turn be fed to $servername() to translate it to the real server name.

Returns:
   > -1   index of server in server list
     -1   window does not exist

Examples:
   $winserv(1)                 returns current server for window #1
   $winserv(main)              returns current server for window "main"
   $winserv()                  returns current server for current window
   $winserv(-2)                window #-2 does not exist, return -1

See Also:
   lastserver(6); myservers(6); servername(6)