Use R default proxy settings

[pierucci]

Like in install.packages().

[pierucci]

So far the way to deal with proxy settings on MS Windows is kind of a hack:

• using httr::GET() alone fails with a timeout error.
• proxy settings must be passed to httr::GET().
• proxy settings are found with curl::ie_get_proxy_for_url(), I think this only return something in MS Windows.
• and then httr::GET() is called with those settings.

On the other hand install.packages() (actually running download.file() under the hood) uses a method argument to handle the connection settings. On MS Windows this method is automatically set to wininet, and that seems to take care of everything.

So ideally I'd like to use something similar with httr::GET() without ressorting to curl::ie_get_proxy_for_url(). But it looks like this method is specific of download.file() and I don't really see how to use it with httr::GET()...

[pierucci]

Rather than that messy proxy script, I'd rather refactor everything with global options. So 1 option, rgho.http_prox, that is either NULL (no proxy) or parsed in a proxy config. Stop the madness.