Changelog re #805
Adding support to shell_env on Windows. Fixes #804

Windows uses the sintax `SET name="value"` that is almost identical to the Linux counterpart.
Tested on Windows 7.
Fixing the test_use_of_path_appends_by_default
Fix for TypeError - convert prompt from unicode to ascii

File "G:\Work\Hpflsk\lib\site-packages\fabric\network.py", line 488, in
prompt_for_password
new_password = getpass.getpass(password_prompt, stream)
File "C:\Python27\Lib\getpass.py", line 95, in win_getpass
msvcrt.putch(c)
TypeError: must be char, not unicode
Changelog, refactor re: #806

Fixes #806