Update portfolios.php

Added order and orderby options to the portfolio shortcode
Update portfolios.php

Sanitized orderby option
Update portfolios.php

Mistake in constructing the argument to orderby - argument is now a space separated string rather than an array.
Allow uppercase arguments to order option

Converts the order option to upper case before checking the value. Allows users to use upper, lower, or a combination in the shortcode and ensures that the argument is uppercased before passed to WP_Query.
Limited orderby option

Update ensures that the `orderby` option is now limited to `author`, `date`, `title`, `rand` and combinations of these seperated by a comma. Invalid keys are skipped, and a space seperated string is created for passing through to `WP_Query`. The array item is unset if no appropriate values are entered so it will pick up the default in `WP_Query`.
Merge pull request #1128 from drjonnicholson/master

Added 'order' and 'orderby' options to portfolio shortcode