Automate lazy generation of REPL completion lists

All invokable methods, slots, signals, and properties visible from
JavaScript, but which do not start with an underscore, are lazily
(only when necessary) added to the completion list through dynamic
reflection.

This leverages `QMetaObject` for reflection of `QObject`s.  As such,
there is now no need to inherit `REPLCompletable` and it has been
removed.

http://code.google.com/p/phantomjs/issues/detail?id=943
New WebPage callback: onResourceError.

This callback is invoked when the WebPage was unable to request the resource

Issue: http://code.google.com/p/phantomjs/issues/detail?id=954
Allow to abort network requests.

Issue: http://code.google.com/p/phantomjs/issues/detail?id=230
Record more changes for the upcoming 1.9.

http://code.google.com/p/phantomjs/issues/detail?id=939