Fix sys.path manipulation

[mgedmin]

Fixes #671, #673. Supersedes #672.

base64 should be imported after sys.path manipulation -- not doing
this causes #671.

sys.path is fixed up at the top level (since commit dde220e),
doing it again in copy_required_modules() breaks things -- this is #673.
This makes the try/finally to restore the old sys.path unnecessary,
which produces the gnarly diff :/

[dstufft]

I had to revert this, because 12.0 was severely broken and nothing I could do seemed to fix it. Details - https://etherpad.openstack.org/p/pydistutils-issues.

[mgedmin]

Quoting that etherpad:

Reverting this commit appears to fix it: dde220e

Yes, that commit was buggy and was the reason why I filed #673. #674 was supposed to fix it! And it worked fine for me when I tested on my Ubuntu 14.10 laptop.

#672 was a different PR that was also supposed to fix #673 (by actually reverting dde220e and replacing it with a different fix for the original bug, which was #625) as well as #671. Have you tried it instead of #674?

Currently virtualenv 12.0.4 is broken:

mg@platonas: ~ $ virtualenv -p /usr/bin/python3 /tmp/py3
Running virtualenv with interpreter /usr/bin/python3
Traceback (most recent call last):
  File "/home/mg/.venv/local/lib/python2.7/site-packages/virtualenv.py", line 8, in <module>
    import base64
  File "/usr/lib/python3.4/base64.py", line 9, in <module>
    import re
  File "/usr/lib/python3.4/re.py", line 324, in <module>
    import copyreg
  File "/home/mg/.venv/lib/python2.7/site-packages/copyreg.py", line 3, in <module>
    from copy_reg import *
ImportError: No module named 'copy_reg'
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 53, in apport_excepthook
    if not enabled():
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 24, in enabled
    import re
  File "/usr/lib/python3.4/re.py", line 324, in <module>
    import copyreg
  File "/home/mg/.venv/lib/python2.7/site-packages/copyreg.py", line 3, in <module>
    from copy_reg import *
ImportError: No module named 'copy_reg'

Original exception was:
Traceback (most recent call last):
  File "/home/mg/.venv/local/lib/python2.7/site-packages/virtualenv.py", line 8, in <module>
    import base64
  File "/usr/lib/python3.4/base64.py", line 9, in <module>
    import re
  File "/usr/lib/python3.4/re.py", line 324, in <module>
    import copyreg
  File "/home/mg/.venv/lib/python2.7/site-packages/copyreg.py", line 3, in <module>
    from copy_reg import *
ImportError: No module named 'copy_reg'

[exited with 1]

which is bug #671.

[dstufft]

I went with existing broken is better then new broken. When I couldn't understand why either one was broken :/