Try PATH.exe in Windows

This fixes tkf/emacs-jedi#148

Author: tkf

python-environment.el

@@ -167,10 +167,12 @@ See `python-environment-make' for how ROOT is interpreted."
 (defun python-environment-bin (path &optional root)
  "Return full path to \"ROOT/bin/PATH\" or \"ROOT/Script/PATH\" if exists.
 ``Script`` is used instead of ``bin`` in typical Windows case.
+In Windows, path with extension \".ext\" may be returned.
 See `python-environment-make' for how ROOT is interpreted."
  (python-environment--existing root
  (concat "bin/" path)
- (concat "Script/" path)))
+ (concat "Script/" path)
+ (concat "Script/" path ".exe")))
 
 (defun python-environment-lib (path &optional root)
  "Return full path to \"ROOT/lib/PATH\" or \"ROOT/Lib/PATH\" if exists.