Issue #20021: use importlib.machinery to import Lib/opcode.py and not an opcode
module coming from somewhere else. makeopcodetargets.py is part of the Python
build process and it is run by an external Python program, not the built Python
program.

Patch written by Serhiy Storchaka.

* Simply use "import opcode" to import the opcode module instead of tricks
  using the imp module
* Use context manager for the output file
* Move code into a new main() function
* Replace assert with a regular if to check the number of arguments
* Import modules at top level

svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r81032 | antoine.pitrou | 2010-05-09 17:52:27 +0200 (dim., 09 mai 2010) | 9 lines

  Recorded merge of revisions 81029 via svnmerge from
  svn+ssh://pythondev@svn.python.org/python/trunk

  ........
    r81029 | antoine.pitrou | 2010-05-09 16:46:46 +0200 (dim., 09 mai 2010) | 3 lines

    Untabify C files. Will watch buildbots.
  ........
................

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r81029 | antoine.pitrou | 2010-05-09 16:46:46 +0200 (dim., 09 mai 2010) | 3 lines

  Untabify C files. Will watch buildbots.
........

should solve the 'failed compile' on the x86 gentoo 3.x buildbot.

on compilers that support it (notably: gcc, SunPro, icc), the bytecode
evaluation loop is compiled with a new dispatch mechanism which gives
speedups of up to 20%, depending on the system, on various benchmarks.