Added override to construct RevisionWalker
Added override to construct RevisionWalker

GNOME/libgit2-glib,weynhamz/GNOME-libgit2-glib,weynhamz/GNOME-libgit2-glib,weynhamz/GNOME-libgit2-glib,chergert/libgit2-glib,GNOME/libgit2-glib,chergert/libgit2-glib,chergert/libgit2-glib,weynhamz/GNOME-libgit2-glib