Implement basic support for times().

The kernel now bills processes for time spent in kernelspace and userspace
separately. The accounting is forwarded to the parent process in reap().

This makes the "time" builtin in bash work.

Kernel/Scheduler.cpp

@@ -181,6 +181,12 @@ bool Scheduler::context_switch(Process& process)
     process.set_ticks_left(time_slice);
     process.did_schedule();
 
+    if (process.tss().cs & 3) {
+        ++process.m_ticks_in_user;
+    } else {
+        ++process.m_ticks_in_kernel;
+    }
+
     if (current == &process)
         return false;