Improve threading on Solaris, according to SF patch #460269, submitted
by bbrox@bbrox.org / lionel.ulmer@free.fr.

This adds a configure check and if all goes well turns on the
PTHREAD_SCOPE_SYSTEM thread attribute for new threads.

This should remove the need to add tiny sleeps at the start of threads
to allow other threads to be scheduled.
diff --git a/pyconfig.h.in b/pyconfig.h.in
index c47a8fb..9250e66 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -214,6 +214,9 @@
 /* The number of bytes in a pthread_t. */
 #undef SIZEOF_PTHREAD_T
 
+/* Defined if PTHREAD_SCOPE_SYSTEM supported. */
+#undef PTHREAD_SYSTEM_SCHED_SUPPORTED
+
 /* Define to `int' if <sys/types.h> doesn't define.  */
 #undef socklen_t