GtkTextView: add some FIXME and TODO comments
Add boolean return value for gtk_text_tag_table_add()

https://bugzilla.gnome.org/show_bug.cgi?id=614717
gtk_text_buffer_create_tag(): return NULL on failure

https://bugzilla.gnome.org/show_bug.cgi?id=614717
textbuffer: fix selection replacement when pasting

It is more logical to first delete the selection and then pasting the
text. When the selection and the text contain tags, the new behavior is
more natural.

A segfault in paste_from_buffer() is also avoided. The segfault occurs when
the text to paste is deleted because it is the selection.

https://bugzilla.gnome.org/show_bug.cgi?id=339539