Prevent OutputPage::addWikiText and friends from causing UNIQ fails

If you transclude a special page, OutputPage::addWikiText can cause
problems. This prevents that from happening, by using a new object
if currently in a parsing operation.

Bug: 14562
Bug: 65826
Change-Id: I7c38fa9e2fbd270e45f73f522612451e77ab8cbb
Merge "Prevent OutputPage::addWikiText and friends from causing UNIQ fails"