Test ability to manipulate a daughter class from its base class wrapper

Even in the case of just creating a `DerivedClass` this test says:
```
swig/python detected a memory leak of type 'DerivedClass *', no destructor found.
```
even though the destructor is defined in the base class.

Author: sethrj

Examples/test-suite/abstract_basecast.i

@@ -0,0 +1,20 @@
+%module abstract_basecast
+
+%inline %{
+class BaseClass {
+public:
+    virtual ~BaseClass() { }
+
+    virtual void g() = 0;
+};
+
+class DerivedClass : public BaseClass {
+public:
+
+    virtual void g() { }
+
+    BaseClass& f() {
+        return *this;
+    }
+};
+%}

Examples/test-suite/common.mk

@@ -102,6 +102,7 @@ C_TEST_BROKEN += \
 # C++ test cases. (Can be run individually using: make testcase.cpptest)
 CPP_TEST_CASES += \
 	abstract_access \
+	abstract_basecast \
 	abstract_inherit \
 	abstract_inherit_ok \
 	abstract_signature \

Examples/test-suite/python/abstract_basecast_runme.py

@@ -0,0 +1,15 @@
+from abstract_basecast import *
+
+def check(flag):
+    if not flag:
+        raise RuntimeError("Test failed")
+
+derived = DerivedClass()
+derived.g()
+check(isinstance(derived, BaseClass))
+check(isinstance(derived, DerivedClass))
+
+base = derived.f()
+base.g()
+check(isinstance(base, BaseClass))
+check(not isinstance(base, DerivedClass))