Use the system proxy when it's defined.
The default HttpUrlConnection does that, as well as okhttp.
This should only work on API v12 and above. Before that the system proxy had to be caught manually by the UrlConnection user.
remove file
Merge branch 'use_android_proxy' of git://github.com/robUx4/AndroidAsync into robUx4-use_android_proxy

Conflicts:
	AndroidAsync/src/com/koushikdutta/async/http/AsyncHttpRequest.java
Refactor proxy implementation. Maybe this should go into ion?

Though HttpUrlConnection behaves the same way, uses proxy automatically.