server.register callback handling does not enforce process.nextTick

[csrl]

According to the hapi style guide, a function taking a callback parameter must enforce the callback is called on process.nextTick.

However, server.register is dependent on whether or not the plugin.register handler calls its 'next' function asynchronously. Since plugin.register takes a 'next' parameter and not 'callback', it creates an inconsistent interface.

See hapijs/glue#72 and somewhat related #2516

server.register 'callback' should be changed to 'next' or it should enforce being called on process.nextTick according to the style guide.