Add test for Glib::Mutex::trylock

Behaviour of this method is different on WIN32

libs/pbd/test/testrunner.cc

@@ -4,11 +4,15 @@
 #include <cppunit/TestResultCollector.h>
 #include <cppunit/TestRunner.h>
 #include <cppunit/BriefTestProgressListener.h>
+#include <glibmm/thread.h>
 #include "scalar_properties.h"
 
+
 int
 main ()
 {
+	Glib::thread_init();
+
 	ScalarPropertiesTest::make_property_quarks ();
 	
 	CppUnit::TestResult testresult;

libs/pbd/wscript

@@ -144,6 +144,7 @@ def build(bld):
         testobj.source       = '''
                 test/testrunner.cc
                 test/xpath.cc
+                test/mutex_test.cc
                 test/scalar_properties.cc
                 test/signals_test.cc
                 test/convert_test.cc