#2 nips2 doesn't compile against GTK+ 2.17.x

[Michael Terry]

Nips2 fails to compile against GTK+ 2.17.x because they are getting more serious about enforcing GtkEntry's private fields. src/gtkitementry.c uses n_bytes and text_size, which are private fields. In 2.17, they have been renamed x_n_bytes and x_n_text_size. So a trivial fix is to #ifdef and use the new name. But that's probably not the right fix. :)

The right fix is using the public API which uses number of characters, not the number of bytes.

For reference, see downstream bug https://bugs.launchpad.net/ubuntu/+source/nip2/+bug/407339