invalid permissions mode is accepted silently

<pre>
bundle agent main
{
files:
"/tmp/foo"
create => "true",
perms => m("22222");
}

body perms m
{
mode => ${x};
}
</pre>

The above is accepted by the parser and runs with strange results:

• Ted observed switching to warn-only mode
• others couldn't replicate that

Please see @tests/acceptance/10_files/01_create/perms-mode.cf@ for the explicit test that verifies "crazy" modes are silently translated.