-fixed bug in py_dist when attempting to convert pkgs installed via pip.
-py_dist now correctly detects cases where the module conversion is not possible.
-added virtualenv detection
-added messages to suggest the user only bootstrap from a venv'd rez install.
-user must explicitly use a --force option in rez-bootstrap to avoid using virtualenv
-added a shell test to make sure that rez cli tools work within a rez-env'd shell