python threads on solaris -- how to get pthread semantics

[Brond Larson]

Is there a supported way to get the python threads packages to build
with 
posix threads on solaris?  By default, the --with-threads configure
switch seems to use native solaris threads.  The difference between
native 
threads and pthreads makes a big difference for fork(2) semantics and
possibly 
other things, and I'd like to be using pthreads on whatever platforms
they are 
available.  By playing with defines and changing link lines I've rebuilt
python to 
use pthreads on solaris, and the tests at least pass, so it doesn't seem
like an 
obviously bad thing to do.  

Can anybody offer insight as to 
(1) why the default is not posix threads whenever they are available on
a platform?  In 
    particular are there known problems on solaris with using posix for
your threads? 
(2) is there an approved way to get posix thread semantics that I'm
missing 
   (unless hacking makefiles is the approved way :-)