Add ptrace functions of job-control and signal

Note that a forked process automatically becomes ptraced state in this
commit.

arch/x86/kernel/cpu.c

@@ -448,6 +448,8 @@ void handle_interrupt(int vector, struct x86_regs *regs)
 
 	check_signal(0, regs);
 	check_need_resched();
+    //kprintf("handle_interrupt,exit\n");
+    //schedule();
 }
 
 void gpe_handler(struct x86_regs *regs)