Log message:
Drop superfluous PKG_DESTDIR_SUPPORT, "user-destdir" is default these days.
Mark packages that don't or might probably not have staged installation.

Log message:
Import boost-threadpool-0.2.5 as wip/boost-threadpool.

threadpool is a cross-platform C++ thread pool library. In general terms thread
pools are an efficient mechanism for asynchronous task processing within the
same process. They realise the thread pool pattern.

A thread pool manages a group of threads in order to process a large number of
tasks. Since multiple threads can be executed in parallel this approach may be
very efficient regarding the overall program performance on many computer
systems. By restricting the number of threads and by reusing them resources are
saved and additionally the system stability is increased.

The threadpool library provides a convenient way for dispatching asynchronous
tasks. Pools can be customized, managed dynamically and easily integrated into
your software.