Allow closures in cdef functions.
Fix error test.
Add preparser tag to test runner.

This allows one to avoid duplicating code, motivated in particular
by the many closure tests.
Test all the closure code with cdef functions as well.
Another closure test.
Fix Python3 next, encoding.
next() already in Py 2.6
Merge branch 'master' of github.com:cython/cython into cdef_closure
Eliminate vtab lookup for unbound methods.
Merge branch 'cdef_closure'