Add a big-ass warning for linux users that can't read.

configure

@@ -324,10 +324,20 @@ fi
 # GTK+ settings
 #
 echo -n "GTK+:    "
-if [ "$GTK" = no ]; then
+if [ "x$GTK" = xno ]; then
   echo "disabled"
 else
   gtk_test
+  if [ "x$GTK" = xno ] && [ "x$SYSTEM" = xLinux ]; then
+      cat <<EOF
+
+*** GTK+ was not found, transmission-gtk will NOT be built.  If you
+*** want to use the graphical version of Transmission" then you will
+*** need to install GTK+ headers and libraries. Try installing looking
+*** for a package called libgtk2.0-dev or gtk2-devel and installing
+*** it, then re-running this script.
+EOF
+  fi
 fi
 
 #