Avoid parser cache miss that often occurs post-save

Avoid parser cache miss that often occurs post-save

* This should not happen as doEditContent() saves the parser cache,
  so only the rare casing if incompatible options should have misses
* The bug could also cause post-save misses with edit stashing
* Avoid the second page parse post-redirect by making sure cache
  timestamps match up instead of calling time() at several points
* Likewise for null edits, which used a different code path
* Removed redundant purge in onArticleCreate() as the new row sets _touched
* Removed pointless purge in onArticleDelete() as there is no row to update
  (the method no-ops in that case to avoid contention already)

Change-Id: I178fe334a3f8691ffd9452bec30561a0c5d37c6c