Preliminary platform-specific flavour support

[ionelmc]

It's primitive now but there could be specialized flavours for: pypy, jython, ironpython (with os variants?)

[ionelmc]

@dstufft So I finally got it to work on Windows ...

Tested this with Python 2.7.9:

C:\Users\ionel_000\Projects\virtualenv>rmdir /S /Q .ve & python -mvirtualenv .ve
Ignoring indexes: https://pypi.python.org/simple
Collecting pip
Collecting setuptools
Installing collected packages: setuptools, pip


Successfully installed pip-6.0.3 setuptools-8.3

C:\Users\ionel_000\Projects\virtualenv>.ve\Scripts\python -c "import sys, pprint; pprint.pprint(sys.path)"
['',
 'C:\\Windows\\SYSTEM32\\python27.zip',
 u'c:\\Python27\\DLLs',
 u'c:\\Python27\\lib',
 u'c:\\Python27\\lib\\plat-win',
 u'c:\\Python27\\lib\\lib-tk',
 u'c:\\Python27\\Scripts',
 u'C:\\Users\\ionel_000\\Projects\\virtualenv\\.ve',
 u'C:\\Users\\ionel_000\\Projects\\virtualenv\\.ve\\lib\\site-packages']

C:\Users\ionel_000\Projects\virtualenv>.ve\Scripts\pip install requests
Collecting requests
  Using cached requests-2.5.1-py2.py3-none-any.whl
Installing collected packages: requests

Successfully installed requests-2.5.1

C:\Users\ionel_000\Projects\virtualenv>.ve\Scripts\python -c "import requests; print requests.get('http://google.com')"
<Response [200]>

[ionelmc]

@dstufft About the move of destination from create to __init__, initially I wanted to have the whole flavouring as specialised subclasses of the builders, but I've moved to a composition patter (the favour being passed to __init__), and I left the change with the destination. There's no huge advantage of having to pass destination everywhere, assuming a builder instance is not reused.

How would you have it?

[dstufft]

So the reason I had destination passed in was so that people could use the builders programmatically and reuse the builders for different virtual environments.