Fixed bugs so now page deletion works again. Also added some minor

Fixed bugs so now page deletion works again.  Also added some minor
safety features:

  o Require deletion confirmation to be sent via POST
    rather than GET.  This makes it slightly more difficult
    to do mass damage via simple scripts...

  o Also include version serialization checks.
    If someone edits the page between when you hit the
    remove button and when you confirm the delete, the
    deletion will fail.  (This also makes it a little harder
    for malicious hackers to trash a wiki...)

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@1653 96ab9672-09ca-45d6-a79d-3d69d39ca109