use sh for virtualenv hooks

	modified:   python/virtualenvs/get_env_details
	modified:   python/virtualenvs/initialize
	modified:   python/virtualenvs/postactivate
	modified:   python/virtualenvs/postdeactivate
	modified:   python/virtualenvs/postmkproject
	modified:   python/virtualenvs/postmkvirtualenv
	modified:   python/virtualenvs/postrmproject
	modified:   python/virtualenvs/postrmvirtualenv
	modified:   python/virtualenvs/preactivate
	modified:   python/virtualenvs/predeactivate
	modified:   python/virtualenvs/premkproject
	modified:   python/virtualenvs/premkvirtualenv
	modified:   python/virtualenvs/prermvirtualenv