fix dmenu prompt in formfiller.sh

util/dmenu.sh breaks with spaces in $DMENU_PROMPT. a proper fix looks
like it will require all scripts that use util/dmenu.sh to use "eval $DMENU"
instead of "$DMENU" (which has side-effects of its own), I'd rather avoid that
for now.

examples/data/scripts/formfiller.sh

@@ -39,7 +39,10 @@ GenForm ()
 GetOption ()
 {
     DMENU_SCHEME=formfiller
-    DMENU_PROMPT="choose profile"
+
+    # util/dmenu.sh doesn't handle spaces in DMENU_PROMPT. a proper fix will be
+    # tricky.
+    DMENU_PROMPT="choose_profile"
     DMENU_LINES=4
 
     . "$UZBL_UTIL_DIR/dmenu.sh"