Taught IDLE's autoident parser that "yield" is a keyword that begins a

stmt.  Along w/ the preceding change to keyword.py, making all this work
w/ a future-stmt just looks harder and harder.

Tools/idle/PyParse.py

@@ -29,6 +29,7 @@ _synchre = re.compile(r"""
     |   except
     |   raise
     |   import
+    |   yield
     )
     \b
 """, re.VERBOSE | re.MULTILINE).search