changed the conditions whether updating references can be enabled or not for rename refactoring except Rename Local Variable (Issue #81)

* the target element should has the enclosing type
* the type is PSR-0 compliant if the type is in the namespace
* the type name equals the file name if the type is not in the namespace (Issue #72)
changed the PDTModelUtils class to use BACK_SLASH constants instead of backslashes