Update drupal_alter() comments in drupal_render_page()

It seems that block_page_alter was used at some point to place the blocks in the renderable array in drupal_render_page.

In common.inc, there is a comment before the invokation of hook_page_alter

  // Modules alter the $page as needed. Blocks are populated into regions like
  // 'sidebar_first', 'footer', etc.
  drupal_alter('page', $page);

and block_install changes the weight of block so that it is the first page_alter called

function block_install() {
  // Block should go first so that other modules can alter its output
  // during hook_page_alter(). Almost everything on the page is a block,
  // so before block module runs, there will not be much to alter.
  db_update('system')
    ->fields(array('weight' => -5))
    ->condition('name', 'block')
    ->execute();
}

However, blocks are now added using block_page_build.

At the very least, the comment in common.inc should be removed. The reordering of weights achieved through block_install might not be necessary anymore either. If it is, the comment should be changed to clarify why.