Add support for maven1 (legacy) request to access a maven2 (default layout) repo

archiva 1.0-alpha-1 doesn't support converting legacy-layout request to default layout. This behaviour is usefull to allow maven1 to access a maven2 repository, and avoid having multiple managed repo as proxies to central.

The attached patch add this support :

• it adds to BidirectionalRepositoryLayout the new method boolean isValidPath( String path )
• it adds to BidirectionalRepositoryLayoutFactory the new method BidirectionalRepositoryLayout getLayoutForPath( String path )
• it use them to detect the layout used by incoming request and build the ArchivaArtifact object used to proxy the request. It aslo overrides the pathInfo to make the request point to the real-file path in the managed repository

BidirectionalRepositoryLayoutFactoryTest also updated