Issue2298

Because of this, for example, setuptools from bundled ensurepipe module generates unix exec files in bin, instead of exe:
jython -m ensurepip
jython pip install yolk
result: 
bin\yolk file created instead of bin\yolk.exe
reason:
systemtools detects windows platform by checking sys.platform for 'win32', while jython sets it to 'java'.
I was able to fix this by adding (os.name == 'java' and os._name == 'nt') everywhere in setuptools sources.
It is huge dealbreaker for windows users who want to use others work

I have tried this out, and it does not work per Aleksei's report:
#!C:\jythondev\jython27\dist\bin\jython.exe
# EASY-INSTALL-ENTRY-SCRIPT: 'yolk==0.4.3','console_scripts','yolk'
__requires__ = 'yolk==0.4.3'
import sys
from pkg_resources import load_entry_point
if __name__ == '__main__':
 sys.exit(
 load_entry_point('yolk==0.4.3', 'console_scripts', 'yolk')()
 )
(It has to be a self executing zip archive to work on Windows.)
Nose, for example, does install correctly on Windows. Different code path presumably.
I have done some work here in the forked versions of pip used by Jython in https://github.com/jythontools/ If you have a patch you would like to contribute against setuptools, that would be useful and you post here.
Next step, we should create a fork of https://bitbucket.org/pypa/setuptools in https://github.com/jythontools/setuptools, which we will bundle as part of the ensurepip bundle; then we can apply, with the eventual goal of upstreaming. (This is very very slow, even for simple stuff.)

Ok, i will prepare PR on github today

Aleksei, I have created a fork of setuptools at https://github.com/jythontools/setuptools, so please submit your PR there. Thanks!

Fixed as of https://hg.python.org/jython/rev/cbb7baea2f3e