Use python3-compatible error reporting in setup.py

Installing from source under Python 3.3 produces:

  Traceback (most recent call last):
    File "setup.py", line 203, in <module>
      print >>sys.stderr, "COULD NOT COPY PRE-BUILT DEPENDENCIES"
  TypeError: unsupported operand type(s) for >>: 'builtin_function_or_method' and '_io.TextIOWrapper'

The problem is the use of the '>>' operator to send a message
to stderr.