Automatically install `pip` when we use conda

[choldgraf]

Since the new version of Anaconda, I believe that warnings will be generated when pipinstalling something if pip is not explicitly installed in the Anaconda environment first. E.g.:

binder-examples/python-conda_pip#1

Do we want to automatically install pip whenever somebody specifies a conda build pack? I can see both sides to this:

• Pros - it continues the behavior that already exists in Binder, and makes a probably reasonable assumption about most people installing anaconda w/ a python env.
• Cons - it makes some decisions on the user's behalf, and one could argue that from a "make it explicit" standpoint, requiring people to put pip in their environment.yml file is preferable

Anyone have thoughts on that?

[betatim]

I wouldn't install it "by magic". We'd have to do some acrobatics around the command where we create the environment for the user and as time goes on people will start listing pip explicitly in their environment.ymls at which point we'd face the problem that we'd want to give users priority but do magic for all others :-/

Especially as it is a warning now I'd wait and see. In the mean time we should update our docs and examples though.

[manics]

The conda/pip question came up in #1038 (comment)
What's the current status- does conda still warn?