Fix an infinite loop in grub-mkconfig

* util/grub.d/10_hurd.in: Make kernel list progression not fail on
kernels whose paths contain regex metacharacters.
* util/grub.d/10_kfreebsd.in: Likewise.
* util/grub.d/10_linux.in: Likewise.
* util/grub.d/20_linux_xen.in: Likewise.

Reported by: Heimo Stranner.

util/grub.d/10_kfreebsd.in

@@ -228,7 +228,7 @@ while [ "x$list" != "x" ] ; do
     kfreebsd_entry "${OS}" "${version}" recovery "-s"
   fi
 
-  list=`echo $list | tr ' ' '\n' | grep -vx $kfreebsd | tr '\n' ' '`
+  list=`echo $list | tr ' ' '\n' | fgrep -vx "$kfreebsd" | tr '\n' ' '`
 done
 
 # If at least one kernel was found, then we need to