GSeekable and GBuffered{In,Out}putStream, GDataOutputStream

[Maciej Marcin Piechotka <uzytkownik2 gmail com>]

Hello,

During discussion on bug #659781[1] a user stated that he cannot use
GDataInputStream as it does not support seeks. After quick look it seems
that adding support for it is relatively easy - the basic patch for
GBufferedInputStream is +117/-4[2].

I can fill a full bug, test etc. but I would like to check first if it
wasn't a deliberate choice. 

Best regards

PS. The patch is proof-of-concept - It might contain off-by-one errors
etc.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=659781
[2] https://bugzilla.gnome.org/attachment.cgi?id=210776