Reverted to using atomic.h on NetBSD
Removed GNU builtins (see http://lists.zeromq.org/pipermail/zeromq-dev/2010-May/003485.html)
Removed SPARC native atomic ops as they are untested and have been commented out for years
Add "memory" to asm clobber for X86 atomic_counter::sub()

Removed various exotic -Wxxx flags in the OpenPGM build to get us to what is actually
required and reasonable; added in -fno-strict-aliasing since OpenPGM generates lots
of warnings about dereferencing typed-punned pointers; removed the OpenPGM extra flags
from libzmq_la_CXXFLAGS and left them only in libzmq_la_CFLAGS so that our code
is not built with the OpenPGM extra flags.

number of application threads to use 0MQ sockets is unlimited; app_threads parameter in zmq_init is unused and obsolete