Implement test for new PyMem_RawMalloc() functions.

tests/run/cpython_capi.pyx

+# mode: run
+# tag: c-api
+
+from cpython cimport mem
+
+
+def test_pymalloc():
+    """
+    >>> test_pymalloc()
+    3
+    """
+    cdef char* m2
+    cdef char* m = <char*> mem.PyMem_Malloc(20)
+    assert m
+    try:
+        m[0] = 1
+        m[1] = 2
+        m[2] = 3
+        m2 = <char*> mem.PyMem_Realloc(m, 10)
+        assert m2
+        m = m2
+        return m[2]
+    finally:
+        mem.PyMem_Free(m)
+
+
+def test_pymalloc_raw():
+    """
+    >>> test_pymalloc_raw()
+    3
+    """
+    cdef char* m
+    cdef char* m2 = NULL
+    with nogil:
+        m = <char*> mem.PyMem_RawMalloc(20)
+        if not m:
+            raise MemoryError()
+        try:
+            m[0] = 1
+            m[1] = 2
+            m[2] = 3
+            m2 = <char*> mem.PyMem_RawRealloc(m, 10)
+            if m2:
+                m = m2
+            retval = m[2]
+        finally:
+            mem.PyMem_RawFree(m)
+    assert m2
+    return retval