Record redirect target in ParserOptions

Since Id44d566a, the text passed to the parser when parsing a
&redirect=no page no longer contains the #REDIRECT directive. For the
benefit of extensions that want to know the redirect target from various
parser hooks, record the target on the ParserOptions object associated
with the parse.

Bug: 62856
Change-Id: Icd1da9911a43eabacbd9e9a369a8326f67f270ff