fixheadtails.eclass can't handle shell scripts so we need to fix ourselves

http://bugs.gentoo.org/152307

--- svscan-add-to-inittab.in
+++ svscan-add-to-inittab.in
@@ -53,10 +53,10 @@
 
 # Splice the new lines into the old file
 {
-  catit | head -$(($lineno-1))
+  catit | head -n $(($lineno-1))
   echo "SV:2345:respawn:$conf_bin/svscan-start /service"
   echo "SX:S016:wait:$conf_bin/svscan-stopall /service"
-  catit | tail +$lineno
+  catit | tail -n +$lineno
 } >"$tmpfile"
 
 # And move it over the existing file