Hard code freeze break request for GtkSourceView

[Sébastien Wilmet <swilmet gnome org>]

Hello,

There was an ABI break in GtkSourceView, because some private functions 
were exported and G_GNUC_INTERNAL has been added to them during this 
cycle [1].

So GtkSourceView needs to bump the soname version. The patch is at [2], 
because GSV was still not using Libtool versioning.

Thanks,
Sébastien

[1] https://bugzilla.gnome.org/show_bug.cgi?id=696412
[2] https://bugzilla.gnome.org/show_bug.cgi?id=477709