Fix auto_activation deactivating non-auto-activated virtualenvs.

With tmp envs this has the unfortunate property of deleting the environment.

Before:
```
Last login: Fri Dec 27 13:39:07 on ttys009
thomasina ♞ :~                                                                  
↪︎ vf tmp
New python executable in /Users/dreid/.virtualenvs/3b4f42e61d463015/bin/python
Installing Setuptools..............................................................................................................................................................................................................................done.
Installing Pip.....................................................................................................................................................................................................................................................................................................................................done.
«3b4f42e61d463015» thomasina ♞ :~                                               
↪︎ vf cd                                                                  1.28s
Removing /Users/dreid/.virtualenvs/3b4f42e61d463015
thomasina ♞ :~/.virtualenvs/3b4f42e61d463015                                   
```

After:
```
Last login: Fri Dec 27 13:39:34 on ttys010
thomasina ♞ :~                                                                  
↪︎ vf tmp
New python executable in /Users/dreid/.virtualenvs/4dee511620ad3669/bin/python
Installing Setuptools..............................................................................................................................................................................................................................done.
Installing Pip.....................................................................................................................................................................................................................................................................................................................................done.
«4dee511620ad3669» thomasina ♞ :~                                               
↪︎ vf cd                                                                  1.24s
«4dee511620ad3669» thomasina ♞ :~/.virtualenvs/4dee511620ad3669                 
↪︎ 
```