autoconf pthreads support

[Mika Raento]

Hiya

Before moving on just to the perl stuff, I noticed that java didn't 
compile for me, due to using '-pthread' hardcoded in Makefile.in. Im not 
quite sure if java has some support for figuring out the right flags for 
itself, but if not, I think acx_pthread would fit us nicely, see:

http://autoconf-archive.cryp.to/acx_pthread.html

	Mika