Python: Teach py/unused-local-variable about nonlocal.

python/ql/test/query-tests/Variables/unused_local_nonlocal/UnusedLocalVariable.expected

@@ -0,0 +1 @@
+| variables_test.py:32:9:32:12 | test | The value assigned to local variable 'test' is never used. |

python/ql/test/query-tests/Variables/unused_local_nonlocal/UnusedLocalVariable.qlref

@@ -0,0 +1 @@
+Variables/UnusedLocalVariable.ql

python/ql/test/query-tests/Variables/unused_local_nonlocal/variables_test.py

@@ -0,0 +1,36 @@
+
+# FPs involving nonlocal
+
+def nonlocal_fp():
+    test = False
+    def set_test():
+        nonlocal test
+        test = True
+    set_test()
+    if test:
+        print("Test is set.")
+
+nonlocal_fp()
+
+def nonlocal_fp2():
+    test = False
+
+    def set_test():
+        nonlocal test
+        test = True
+    set_test()
+    result = 5
+    if not test:
+        return
+    return result
+
+def not_fp():
+    test = False
+    def nonlocal_test():
+        nonlocal test
+    def set_test():
+        test = True
+    nonlocal_test()
+    set_test()
+    if test:
+        print("Test is set.")