Lots of polishing, organizational changes, bug fixes, error handling etc. are
introduced.
COPY and NEW space thread creation are allowed but not thoroughly tested yet. It
seems they will work best if the lib supports utcb virtual range management
through the mapping.
UTCB support has beed added. It has the same drawback as in the stack support:
the area in question has to be already mapped-in.
There are also some minor fixes for the stack support and the utcb common helper
routines.
This is one of the steps we need in the process of providing a similar interface
for thread creation which can be found in the mainstream operating systems like
Linux.
