Better support for dialog options plus other improvements.

This is a general collection of useful changes I've made. Some could be split into their own patches if desired.

The jQuery UI dialog API support a bunch of useful options that are difficult to apply.

This patch exposes the dialog options in a few places.

It also uses those options to stop the dialog from resizing when it goes from a currently open state, to a loading state. This is desirable when you have paged content inside a dialog and don't want it to constantly keep resizing.

It also adds a class to the dialog container when it has buttons.

Also, the patch exposes a new 'hook' of sorts that allow forms created with dialog_get_form() to still have custom options applied. The use case is when you create a menu router item that uses dialog_get_form() as the page callback. Any module can implement [form_id]_dialog_options() and return an array of options to be applied. I'm up for discussing this, perhaps a general dialog_options_alter, or just hook_dialog_options would be more generic and multiple modules could affect the same form easier.

Finally, support for $form_state['redirect'] is added to dialog_get_form().