* Command to activate virtualenvs on changing directory
Enables automatic activation of a virtualenv when jumping into a directory
This is done by looking in the current directory for a file or directory
named `.venv`. If it's not found in the current directory its parents will
also be examined. `.venv` can be either:
1. A file containing the name of a virtualenv found in $WORKON_HOME
2. A directory containing bin/activate (meaning that the directory is
assumed to be a virtualenv.)
If $WORKON_HOME is set it is assumed that virtualenvwrapper is installed
and the `workon` command will be issued.
This shouldn't cause problems for anyone and should improve startup times for
anyone using python with virtualenvwrapper because it will wait for the first
command to load rather than right away.
* Support skip-virtualenvwrapper-init zstyle in python module to avoid auto-sourcing of virtualenvwrapper.sh
* Don't overwrite the WORKON_HOME env var if the user has already set it
