Update PATH after installing git

Currently there exists no way to automatically update the PATH variable after installing a chocolatey package. There is [a ticket #134](https://github.com/chocolatey/chocolatey/issues/134) in their bugtracker.

Current workaround may include starting the new PowerShell processes [through pure .NET](http://stackoverflow.com/questions/8761888/powershell-capturing-standard-out-and-error-with-start-process) because I cannot see another way of using the new (modified) environment inside initial process.