fix ticket #145 also for CondExprNode, make "bint (+) non-bint -> object" a general rule for independent spanning type finding, merge duplicated type determination functionality from CondExprNode back into PyrexTypes.py

native support for Py_UNICODE, coercion between 1-character unicode literals and Py_UNICODE, fix C iteration over unicode strings by using Py_UNICODE*

__Pyx_PyObject_IsTrue now has only a single branch, even at -O0.
(The bitwise | is intentional.) This is only a 2.5% or so speedup
in my microbenchmarks, but it's something.

Implemented like typedef.