Minor comments updates.
Add some TODOs about VariantDict.

We should remove Application::add_main_option_entries() and
add_option_group() if we cannot get the handle_local_entries signal
and its VariantDict right.
extra_defs: Add some new gio classes.

* tools/extra_defs_gen/generate_defs_gio.cc:
* tools/extra_defs_gen/generate_defs_glib.cc:
  Mention some recently-added GTypes.
* gio/src/gio/gio_signals.defs: Regenerate.
genereate_defs_glib: Add some more glib GTypes.

Though we don't actually use them or need to use them.
Still, it would be nice to see when something changes about these
types.
Add Glib::VariantDict, needed for GApplication.

* glib/src/filelist.am:
* glib/src/variantdict.[hg|ccg]: Add it as a generic refcounted
  type, with templated lookup_value() and insert_value() methods,
  though these are completely untested so far.
* glib/src/variant.hg: Ignore a g_variant_dict_* function that
  gmmproc thinks is part of Variant.
* tools/m4/convert_gio.m4:
* tools/m4/convert_glib.m4: Move all Variant* conversion to the
  glib conversions and add a necessary one.
* glib/glibmm.h: Include variantdict.h.
Add a TODO comment
Application, ApplicationCommandLine: Wrap API that uses VariantDict.

* gio/src/application.hg: Add the handle-local-options signal.
* gio/src/applicationcommandline: Add get_options_dict().
* tools/m4/convert_glib.m4: Add necessary conversions.

I really need to try using this API so we can be sure that it
is correct before calling it stable, because this part of the awful
GApplication documentation is particularly awful.
Regenerated *_docs.xml files.
Application, ApplcationCommandLine: #include variantbase.h

This was a problem when building gtkmm and would probably have
been shown by a test case in glibmm.
Variant: Remove the now-unnecessary local g_variant_parse_error_quark().

This is in glib itself now:
https://git.gnome.org/browse/glib/commit/glib/gvariant.h?id=eeac91f866939fd033303f34c7eb9d2b57c769fb
and was causing segfaults.

Bug #727554 (Antoine Jacoutot)
VarantDict::lookup_value(): Add a missing return.
VariantDict::lookup_value(): Return soon enough on failure.
Application: Remove add_option_entries().

Because it seems useless. We need a new function, I think.
See glib bug:
https://bugzilla.gnome.org/show_bug.cgi?id=727602
Application: Comment out an implementation too.
Keyfile: Add save_to_file().
Settings: Add get_user_value() and get_default_value().
Socket: Add get/set_option().
TlsInteraction: Add certificate request methods.

* gio/src/tlsinteraction.hg: Add invoke_request_certificate(),
  request_certificate(), request_certificate_async() and
  request_certificate_finish().
2.39.93
Visual Studio Builds: Update glibmm Project

Add the newly-added variantdict.[cc|h] sources into the build, so that the
build of glibmm is complete.