6/22/2008:
 
Erubis modified:
* <%= %> now can take a block, so <%= helper do %>Hello<% end %> now works
* Erubis buffer is now an ivar (@_erb_buf), which eliminates the need for
  eval in capture helpers.
  
CONSEQUENCE:
Helpers that take a block should simply return a string, and should not
use concat. Example:
  
  def my_helper(&blk)
    "My helper says #{capture(&blk)}."
  end