Use vim's index() function to find values in a list

.. this expresses the intent to test for presence-in-list more clearly
than a manually written for-loop.
Merge pull request #14 from muggenhor/list-index

Use vim's index() function to find values in a list
allow user to disable internal modelines warning

- if ‘g:secure_modelines_verbose’  is true but not greater than one,
don’t display the initial warning message about
forcibly disabling internal modelines