#2021 - Cleanup thumb_dirty and resize_dirty instances.

- g2_import: changed "false" assignment to "0" assignment for consistency.
- admin_theme_options: removed unused variables (they're called/used nowhere else).
- graphics: removed stanza that clears thumb_dirty and resize_dirty and returns
if we have no ops.  This has no effect on Gallery currently (for one,
graphics::generate doesn't normally get called on an item with no dirty flags),
but can inconsistently set resize_dirty of albums and movies to 0 where it's
otherwise left at 1.  Going forward, it may be useful to be consistent here.
- gallery_installer: added v57 stanza to correct any resize_dirty flags of
movies/albums that were previously reset to 0.
- module.info, install.sql: update to v57