LightWeight http wagon not thread-safe

Aether (maven3) by default parallelized metadata resolution on 4 threads (aether.metadataResolver.threads) and artifacts downloading on 5 (maven.artifact.threads).
In such context, Wagon is not used sequentially.
LightWeightHttpWagon is designed for mono-thread, sequential usage. It rely on system properties and on setting/resetting java.net.Authenticator singleton.
The result is that, in some cases (typically : when settings defines many repositories with various credentials), credentials may not apply and download will fail

A potential fix is

• to use Java5 URL.openConnection(Proxy) instead of using system properties
• to use a shared, singleton java.net.Authenticator that lookup repositories to match the requested URL