Python: Address review comments

- changes `getReceiver` to `getObject`
- fixes `calls` to avoid unwanted cross-talk
- adds some more documentation to highlight the above issue

python/ql/test/experimental/dataflow/method-calls/test.expected

@@ -0,0 +1,8 @@
+conjunctive_lookup
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj1 | bar |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj1 | foo |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj2 | bar |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj2 | foo |
+calls_lookup
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj1 | foo |
+| test.py:6:1:6:6 | ControlFlowNode for meth() | meth() | obj2 | bar |

python/ql/test/experimental/dataflow/method-calls/test.py

@@ -0,0 +1,6 @@
+if cond:
+    meth = obj1.foo
+else:
+    meth = obj2.bar
+
+meth()

python/ql/test/experimental/dataflow/method-calls/test.ql

@@ -0,0 +1,18 @@
+import python
+import semmle.python.dataflow.new.DataFlow
+import experimental.dataflow.TestUtil.PrintNode
+
+query predicate conjunctive_lookup(
+  DataFlow::MethodCallNode methCall, string call, string object, string methodName
+) {
+  call = prettyNode(methCall) and
+  object = prettyNode(methCall.getObject()) and
+  methodName = methCall.getMethodName()
+}
+
+query predicate calls_lookup(
+  DataFlow::MethodCallNode methCall, string call, string object, string methodName
+) {
+  call = prettyNode(methCall) and
+  exists(DataFlow::Node o | methCall.calls(o, methodName) and object = prettyNode(o))
+}