* added mutex trylock regression test

projects/test_mutex_trylock_fail/Jamfile

+SubDir TOP projects test_mutex_trylock_fail ;
+
+Module test_mutex_trylock_fail : main.c ;
+
+UseModule test_mutex_trylock_fail ;

projects/test_mutex_trylock_fail/main.c

+#include <stdio.h>
+#include <mutex.h>
+
+#include <thread.h>
+#include <flags.h>
+#include <kernel.h>
+
+mutex_t mutex;
+
+void second_thread(void) {
+    puts(" 2nd: trying to lock mutex...");
+    mutex_trylock(&mutex);
+    puts(" 2nd: done.");
+}
+
+tcb second_tcb;
+char second_stack[8192];
+
+int main(void)
+{
+    puts("main: locking mutex...");
+    mutex_lock(&mutex);
+
+    puts("main: creating thread...");
+    int pid = thread_create(&second_tcb, second_stack, 8192, PRIORITY_MAIN-1, CREATE_STACKTEST, second_thread, "nr2");
+    
+    puts("main: thread created. Unlocking mutex...");
+    mutex_unlock(&mutex, true);
+
+    puts("main: mutex unlocked.");
+}

projects/test_mutex_trylock_fail/tests/test_mutex_trylock_fail

+#!/usr/bin/expect
+
+set timeout 5
+
+spawn pseudoterm $env(PORT) 
+
+expect { 
+    "main: mutex unlocked." {} 
+    timeout { exit 1 }
+}
+
+puts "\nTest successful!\n"
+