Refactored entity object resolution.

The IPA.get_entity() has been modified to accept either entity name
or entity object. If it receives an entity object it will return
the object itself. Otherwise, it will resolve the name in the entity
registry.

The other_entity variables have been modified to store a reference
to the entity object instead of its name. The test cases have been
modified to use real entity objects instead of just the names.

Ticket #2042

install/ui/test/ordered_map_tests.html

@@ -4,7 +4,6 @@
     <title>Ordered Map Test Suite</title>
     <link rel="stylesheet" href="qunit.css" type="text/css" media="screen">
     <link rel="stylesheet" type="text/css" href="../jquery-ui.css" />
-
     <script type="text/javascript" src="qunit.js"></script>
     <script type="text/javascript" src="../jquery.js"></script>
     <script type="text/javascript" src="../jquery.ordered-map.js"></script>