Lots of hacking:

- Turn Keyboard into a CharacterDevice (85,1) at /dev/keyboard.
- Implement MM::unmapRegionsForTask() and MM::unmapRegion()
- Save SS correctly on interrupt.
- Add a simple Spawn syscall for launching another process.
- Move a bunch of IO syscall debug output behind DEBUG_IO.
- Have ASSERT do a "cli" immediately when failing.
  This makes the output look proper every time.
- Implement a bunch of syscalls in LibC.
- Add a simple shell ("sh"). All it can do now is read a line
  of text from /dev/keyboard and then try launching the specified
  executable by calling spawn().

There are definitely bugs in here, but we're moving on forward.

Kernel/Task.h

@@ -90,6 +90,7 @@ public:
     int sys$geterror() { return m_error; }
     void sys$sleep(DWORD ticks);
     void sys$exit(int status);
+    int sys$spawn(const char* path);
 
     struct
     {