Add corner case temp (de)allocation test.

This is as simple as I could get it.

tests/run/temps_corner1.pyx

+__doc__ = """
+   >>> B().coeffs_bitsize()
+   [2]
+"""
+
+cdef class A:
+    def numerator(self):
+        return self
+
+cdef int  bitsize(A a):
+    return 1
+    
+coeffs = [A()]
+
+class B:
+    def coeffs_bitsize(self):
+        r = [bitsize(c.numerator())+1 for c in coeffs]
+        return r