Add testcase for failing namespace switch throwing exception from a module.

Issue #290. This currently fails, to draw attention to the issue.

tests/basics/import1b.py

@@ -1 +1,4 @@
 var = 123
+
+def throw():
+    raise ValueError

tests/basics/try-module.py

@@ -0,0 +1,15 @@
+# Regression test for #290 - throwing exception in another module led to
+# its namespace stick and namespace of current module not coming back.
+import import1b
+
+def func1():
+    return
+
+def func2():
+    try:
+        import1b.throw()
+    except ValueError:
+        pass
+    func1()
+
+func2()