[3213] added more comments about the use of sw_vers and os/ver based check.

configure.ac

@@ -233,6 +233,11 @@ case "$host" in
 
 	# In OS X 10.9 (and possibly any future versions?) pthread_cond_destroy
 	# doesn't work as documented, which makes some of unit tests fail.
+	# Testing a specific system and version is not a good practice, but
+	# identifying this behavior would be too heavy (running a program
+	# with multiple threads), so this is a compromise.  In general,
+	# it should be avoided to rely on 'osx_version' unless there's no
+	# viable alternative.
 	osx_version=`/usr/bin/sw_vers -productVersion`
 	if [ test $osx_version = "10.9" ]; then
 		bind10_undefined_pthread_behavior=yes