Rework the internal lock interface

With this patch, the 'futex' syscall gets used for blocking and unblocking
of threads in the Linux-specific lock implementation.

The 'Native_thread_id' type, which was previously used in the
lock-internal 'Applicant' class to identify a thread to be woken up,
was not suitable anymore for implementing this change. With this patch,
the 'Thread_base*' type gets used instead, which also has the positive
effect of making the public 'cancelable_lock.h' header file
platform-independent.

Fixes #646.

base-codezero/include/base/ipc_pager.h

@@ -147,7 +147,7 @@ namespace Genode {
 			/**
 			 * Return badge for faulting thread
 			 */
-			unsigned long badge() const { return _last.tid; }
+			unsigned long badge() const { return _last; }
 
 			/**
 			 * Return true if page fault was a write fault