tests/basics: Add test for use of return within try-except.

The case of a return statement in the try suite of a try-except statement
was previously only tested by builtin_compile.py, and only then in the part
of this test which checked for the existence of the compile builtin.  So
this patch adds an explicit unit test for this case.

tests/basics/try_return.py

+# test use of return with try-except
+
+def f(l, i):
+    try:
+        return l[i]
+    except IndexError:
+        print('IndexError')
+        return -1
+
+print(f([1], 0))
+print(f([], 0))