Add support for Mac os x 10.8.2 's bash

1. osx 10.8.2 has python 2.5/6/7 but don't have link any one of them to python2,
   so i hard code as Python2.7, please update it if you have good idea :-)

2. prompt symbol display error in osx's bash, I add new group names "macosx"
   and code to detect os type, now it works in osx well