closed #4419,  Backup the environment  file when adding environment variable in setup.py.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into develop
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into develop
Merge pull request #5882 from natural-law/develop

Backup the environment  file when adding environment variable in setup.py.