_dumbwin32proc breaks with unicode environmental variables

New submission from ivank <[email protected]>:

Windows supports unicode environmental variables. pywin32 supports spawning processes with str or unicode environmental variables, but not a mix of them:

{{{
...
  File "C:\Python26\lib\site-packages\twisted\internet\utils.py", line 25, in _callProtocolWithDeferred
    reactor.spawnProcess(p, executable, (executable,)+tuple(args), env, path)
  File "C:\Python26\lib\site-packages\twisted\internet\posixbase.py", line 234, in spawnProcess
    return Process(self, processProtocol, executable, args, env, path)
  File "C:\Python26\lib\site-packages\twisted\internet\_dumbwin32proc.py", line 176, in __init__
    doCreate()
  File "C:\Python26\lib\site-packages\twisted\internet\_dumbwin32proc.py", line 174, in doCreate
    command, cmdline, None, None, 1, 0, env, path, StartupInfo)
exceptions.TypeError: All dictionary items must be strings, or all must be unicode
}}}

This problem and "solution" is sort of documented here:
https://realityforge.vrsource.org/viewvc/maestro/trunk/maestro/daemon/plugins/services/launch/process.py , near "win32process.CreateProcess requires that all environment keys and"

This bug causes a lot of test failures with twisted.web2 on Windows Vista or Windows 7. The default install of Python 2.6.2 on these operating systems introduces environmental variables with unicode values:

C:\>python -c "import Tkinter, os; exec 'for k, v in os.environ.iteritems():\n\tif isinstance(v, unicode): print k, v'"
TK_LIBRARY C:\Python26\tcl\tk8.5
TIX_LIBRARY C:\Python26\tcl\tix8.4.3
TCL_LIBRARY C:\Python26\tcl\tcl8.5

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Type     : defect
Component: core
Keywords : 
Priority : normal
Nosy     : 
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http://twistedmatrix.com/trac/ticket/3964