Don't quote ${SH} (#1240)

When ${SH} is quoted one cannot replace the shell with another shell with
arguments, e.g., for debugging purposes: SH="sh -x" bastille ...
Don't quote, expect the shell path to never contain a space and be from /etc/shells.

This fixes #1240

usr/local/bin/bastille

@@ -240,7 +240,7 @@ if [ -f "${SCRIPTPATH}" ]; then
 
     : "${SH:=sh}"
 
-    exec "${SH}" "${SCRIPTPATH}" "$@"
+    exec ${SH} "${SCRIPTPATH}" "$@"
 
 else
     error_exit "${SCRIPTPATH} not found."