- Adds drupal_set_header() and drupal_get_headers().
- Cache now stores custom headers.
- Replace theme_head() with drupal_get_html_head(), added drupal_set_html_head().
- Added RSS autodiscover links to node, blog and taxonomy pages.
+ Changed drupal_page_header(): converts the If-Modified-Since header into a
timestamp and compares against the cache data. Ignore If-Modified-Since
and ETag headers if they are present but empty.
+ Few minor other code cleanups.