Adapt to our non-GNU grep

--- util/fluxbox-generate_menu.in.orig	Sun Feb  8 04:44:45 2015
+++ util/fluxbox-generate_menu.in	Mon Feb  9 04:26:49 2015
@@ -330,7 +330,7 @@ searchForIcon(){
     # echo "^.${entry_exec}.[[:space:]]*<.*/${icon_base}\....>" 
     if [ -f "$entry_icon" ]; then
     # if icon exists and entry does not already exists, add it
-        if ! grep -q -m 1 "^.${execname}.[[:space:]]*<.*/${icon_base}\....>" $ICONMAPPING 2> /dev/null; then
+        if ! grep -q "^.${execname}.[[:space:]]*<.*/${icon_base}\....>" $ICONMAPPING 2> /dev/null; then
             printf "\"${execname}\" \t <${entry_icon}>\n" >> $ICONMAPPING
         else 
             : echo "#    mapping already exists for ${execname}" >> $ICONMAPPING