migrationitem: add support for using items as indexes in to lists

In order to provide the support, items may now be tested for equality
and hashed.  Two items are considered equal if they have the same
unversioned name (and version, if appropriate); hashing is based on
a tuple hash of the name and version.

Signed-off-by: Adam D. Barratt <adam@adam-barratt.org.uk>

migrationitem.py

@@ -29,6 +29,19 @@ class MigrationItem:
         else:
             return self.uvname
 
+    def __eq__(self, other):
+        isequal = False
+        if self.uvname == other.uvname:
+            if self.version is None or other.version is None:
+                isequal = True
+            else:
+                isequal = self.version == other.version
+
+        return isequal            
+
+    def __hash__(self):
+        return hash((self.uvname, self.version))
+
     def _get_name(self):
         return self._name