Coercion fix

src/org/python/core/PySliceDerived.java

Index: src/org/python/core/PySliceDerived.java
===================================================================
--- src/org/python/core/PySliceDerived.java	(revisión: 5129)
+++ src/org/python/core/PySliceDerived.java	(copia de trabajo)
@@ -1111,6 +1111,20 @@
         return super.__tojava__(c);
     }
 
+    public Object __coerce_ex__(PyObject o) {
+        PyType self_type=getType();
+        PyObject impl=self_type.lookup("__coerce__");
+        if (impl!=null) {
+            PyObject res=impl.__get__(this,self_type).__call__(o);
+            if (res==null||res==Py.None)
+                return res;
+            if (!(res instanceof PyTuple))
+                throw Py.TypeError("coercion should return None or 2-tuple");
+            return((PyTuple)res).getArray();
+        }
+        return super.__coerce_ex__(o);
+    }
+
     public String toString() {
         PyType self_type=getType();
         PyObject impl=self_type.lookup("__repr__");