RFR 7125055: ContentHandler.getContent API changed in error

[chris hegarty]

During some of the warning cleanups the method declaration of the public 
platform API java.net.ContentHandler.getContent(URLConnection, Class[]) 
was incorrectly changed. This CR proposes to revert this change fix 
appropriate subclasses, so as not to re-introduce warnings in this area.

http://cr.openjdk.java.net/~chegar/7125055/webrev.00/webrev/
-Chris.