* The status variable is redundant

* Remove PATH modification from check_pathvar
* Rename check_pathvar to check_system_path
* Add conda_prepend_bin function to handle PATH modification during activation
* Add logic to handle first-run activation, and subsequent calls to change conda environments (otherwise conda clobbers its own shell functions)
* Use $CONDA_PYTHON_EXE and $CONDA_EXE to ensure conda comes from the just-installed tree

* check_pathvar was the culprit