Doing next(IfParser()) works for Python 2.7, because it calls
IfParser.next(), but in Python 3 will call IfParser.__next__() which does
not work since it is not an iterator and does not have that method.
Thanks to Chris Beaven for the initial patch, Fredrik Lundh for the basis
of the parser methodology and Russell Keith-Magee for code reviews.
There are some BACKWARDS INCOMPATIBILITIES in rare cases - in particular, if
you were using the keywords 'and', 'or' or 'not' as variable names within
the 'if' expression, which was previously allowed in some cases.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@11806 bcc190cf-cafb-0310-a4f2-bffc1f526a37