- Block and theme improvements. Patch by Ax.

   + block_list() (in block.module): returns an array of block objects for
     $region.
   + theme_blocks() (in theme.inc): uses block_list() and theme("block") to
     actually render them.

  Advantages:
   + Decouples blocks content and layout, allows block_list() to be used
     for non-output purposes (think "pull").
   + Unifies naming in theme.inc: render_blocks()) didn't really fit there.
   + Puts block_list() in blocks.module where it logically belongs.

- Removed some cruft from the Xtemplate theme.  Patch by Ax.