Pypi install

Improving integration between conda and pip: 

  1) Enhancing conda list to show pip installed packages
  2) Adding fallback to pip install if conda install fails
  3) Adding --use-pypi flag to conda install which will 
       a) run conda skeleton
       b) run conda build
       c) run conda install 
  4) Improve the "file lock" mechanism so that calling back into conda from same process still works.