Use default location of FvwmMFL socket in FvwmCommand.

  FvwmCommand has to be explicitly told where the FvwmMFL
  socket is. Make it so FvwmCommand uses the default location
  of the FvwmMFL socket if FVWMMFL_SOCKET is not set, or
  the -f <socket> option isn't used.

bin/FvwmCommand.in

@@ -18,11 +18,18 @@ def mflclnt(verbose, read_from_stdin, info, fvwm_socket, args):
     sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
 
     # Connect the socket to the "port" where the server is listening
-    # FvwmMFL is setting this in environment, so we can really treat
-    # absence of the environment FVWMMFL_SOCKET as error, except when
-    # explicit -f <sockname> has been specified by the user.
+    # FvwmMFL is setting this in environment. This is done by using
+    # the explicit -f <sockname> flag if it is provided, otherwise
+    # use the environment FVWMMFL_SOCKET if it is defined, then fall
+    # back to TMPDIR/fvwm_mfl.sock if TMPDIR is defined, and last use
+    # the default location /tmp/fvwm_mfl.sock.
     if not fvwm_socket:
-        fvwm_socket = str(os.environ.get('FVWMMFL_SOCKET'))
+        if 'FVWMMFL_SOCKET' in os.environ:
+            fvwm_socket = str(os.environ.get('FVWMMFL_SOCKET'))
+        elif 'TMPDIR' in os.environ:
+            fvwm_socket = str(os.environ.get('TMPDIR')) + '/fvwm_mfl.sock'
+        else:
+            fvwm_socket = '/tmp/fvwm_mfl.sock'
         def_socket = True
     else:
         def_socket = False