Drupal 6.31 via cherry-pick

fixes #82
Merge pull request #83 from pressflow/SA-CORE-2014-002

Drupal 6.31 via cherry-pick
Fix #84 by using drupal_page_is_cacheable()
Merge pull request #85 from pressflow/SA-CORE-2014-002-fix

Fix #84 by using drupal_page_is_cacheable()
Merge remote-tracking branch 'upstream/master'

Conflicts:
	modules/system/system.module
merged pressflow-6.31.114