Implement GitHub SSL check

[jdfreder]

I've added a shell for it, the code just needs to be filled in now.

Background: Some corporate networks block the GitHub git protocol, @SylvainCorlay . The goal of this check is to test to see if the connection is blocked, and if it is blocked, warn the user ahead of time. Suggest to the user git config --global url."https://github".insteadOf git://github or git config --global url."https://".insteadOf git:// ... Or even better, prompt the user and then do it for them if they agree!!!

To prompt, we can use the handy-dandy this.yesNo function in the StepBase.