Include data format when requesting a published block

The content of some Drupal 7 blocks are returned as render arrays. Other D7 sites can render those, but D6 sites cannot.

In the D7 version, add another argument to the sharedblocks/%/% menu callback to specify the format. In sharedblocks_fetch_block(), tack array at the end of the URL.

In sharedblocks_publish_block(), check this new argument. If it's 'array' (as it will be when D7 sites are requesting the block), encode the $block array as-is; otherwise, assume that the requesting site cannot handle render arrays, and render $block['content'] if it is an array, before encoding it.