Fix #14, use correct pointer type

Author: Devon Ryan

py2bit.c

@@ -32,9 +32,9 @@ static PyObject *py2bitOpen(PyObject *self, PyObject *args, PyObject *kwds) {
 }
 
 PyObject *py2bitEnter(pyTwoBit_t *self, PyObject *args) {
-    pyTwoBit_t *pytb = self->tb;
+    TwoBit *tb = self->tb;
 
-    if(!pytb) {
+    if(!tb) {
         PyErr_SetString(PyExc_RuntimeError, "The 2bit file handle is not open!");
         return NULL;
     }