Workaround the load of OVCCGtkMessageInfo as type-func seems currently
sort-of broken (unused), by pre-loading the type forcefully.
See: https://bugzilla.gnome.org/show_bug.cgi?id=786932

This makes OVCCGtkBoard a more normal widget by allowing to change the
OVCCBoard it displays, avoiding the need to create and destroy the
widget.

This gives better consistency by having tile and pawn related signals
next to each other, as well as making the board more self-sufficient
with it getting signals for all changes on it.

Now we don't install other data next to the link, we must make sure the
directory is created.

Make variable "$<" in non-suffix rules is a GNU Make extension, so
switch to suffix rules.

Additionally, make the rules a little more generic by extracting custom
flags to a _FLAGS variable.

Also drop the build-time support for vertical layout, it's useless,
less nice, adds complexity and needs different packing options.

Add an icon for the application, based on the tile 13 by Salomé.

We use libgthread, but we didn't explicitly link it.  This used to
work because other libraries we link also links libgthread, but such
indirect dependencies are rejected by modern linkers.

Automake warns us that building subdir object without the subdir-object
option will break in the future;  and putting objects in the right
directory is a good thing anyway.

Automake changes its warnings from versions to versions, and they
generally are actually harmless, but can prevent generation of the
build system files.  So, still display all warnings, but do not
treat them as errors.

Also, make newer Automake happy by calling AM_PROG_AR if available.