The test case that I put in there already doesn't cover this? 

When building a machine that will be shared amongst users its a lot easier for certain variables to be set on the system level. In this particular case with Git 1.8.5 we want to override the `http.proxy` for only our internal GitHub Enterprise installation. Everything else should use the normal, external proxy. The same goes for SSL verification.  Since we're going through a MITM proxy we turn it off.