test_popen fails in 2.5c2. The reason is that popen invokes

cmd.exe /c "c:\program files\python25\python.exe" -c
"import sys;print sys.argv"

cmd.exe does not support that syntax, and gives an
error (which silently disappears); the pipe read then
returns an empty string.

This problem exists atleast since Python 2.3.

To fix this, cmd.exe needs to be invoked as

cmd.exe /c "c:\program files\python25\python.exe" -c
"import sys;print sys.argv"

The attached patch fixes this by always wrapping the
command line with an addition pair of quotes.

It's not clear to me whether this can go into 2.5.1: an
application may already work around this problem by
passing extra quotes to popen, which would then break
if popen adds even more quotes.