Fix most trivially-findable print statements.

There's one major and one minor category still unfixed:
doctests are the major category (and I hope to be able to augment the
refactoring tool to refactor bona fide doctests soon);
other code generating print statements in strings is the minor category.

(Oh, and I don't know if the compiler package works.)

Lib/warnings.py

@@ -193,7 +193,7 @@ def _processoptions(args):
         try:
             _setoption(arg)
         except _OptionError as msg:
-            print >>sys.stderr, "Invalid -W option ignored:", msg
+            print("Invalid -W option ignored:", msg, file=sys.stderr)
 
 # Helper for _processoptions()
 def _setoption(arg):