Porting from the 2.0 to 2.2 series of c++-gtk-utils
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The 2.2 series makes few API changes to the 2.0 series.  It is mainly
intended to enable some bugs to be fixed and simplifications to be
made which require ABI rather than API change (by altering object
layout), and to provide a generic callable object interface for
Callback::post(), start_iowatch(), start_timeout(),
Emitter::connect(), Future::fail(), Future::when(),
Notifer::connect(), SafeEmitter::connect(), TaskManager::add_task(),
TaskManager::make_task_when(), TaskManager::make_task_when_full(),
TaskManager::make_task_compose() and Thread::start(), which requires
gcc-4.6 or later.

However one transitional API feature has been dropped: the
--with-auto-ptr configuration option (intended to provide some source
compatibility between the 1.2 and 2.0 series) has been removed.

The previously deprecated Callback::make_val() functions are retained
for API compatibility reasons, but are no longer documented.  For any
code which used Callback::make_val(), Callback::make_ref() should be a
more efficient drop-in replacement.
