Especially the gtk_*_type ones in gtktexttypes.h were mentioned in
gtk.symbols presumably by accident. That header isn't even installed,
so no way can they be supposed to be public.
gtk_text_attr_appearance_type is from the installed but "semi-private"
gtktextlayout.h, so drop that one too from gtk.symbols for now.
The use of gtk_text_unknown_char_utf8 is bit of a mess. Code in a few
files knew implicitly that it is three bytes. Define a symbolic name
for the length of it instead. Add an exported function
gtk_text_unknown_char_utf8_gtk_tests_only() that returns a pointer to
it just for the sake of gtk/tests/textbuffer.c. Prefix the variable
with an underscore.
I doubt the usefulness of the test_utf8() in textbuffer.c. If it could
be dropped, gtk_text_unknown_char_utf8_gtk_tests_only() could be
dropped, too.
Preferrably should be made just into a local variable for libgtk like
_gdk_debug_flags for libgdk. But for now used by
gtk/tests/textbuffer.c and modules/printbackends/cups/gtkprintbackendcups.c.
Special case \r\n in gtk_text_buffer_backspace since \r should not be
reinserted even if we are deleting one char at a time. Also add
corresponding unit test. Fixes bug #544724.
