Enable routing of thread events to signal contexts via
Kernel::route_thread_event.
Replace Kernel::set_pager by Kernel::route_thread_event.
In base-hw a pager object is a signal context and a pager activation
is a signal receiver. If a thread wants to start communicating its page
faults via a pager object, the thread calls Kernel::route_thread_event with
its thread ID, event ID "FAULT", and the signal context ID of the pager object.
If a pager activation wants to start handling page faults of a pager object,
the pager activation assigns the corresponding signal context to its signal
receiver. If a pager activation wants to stop handling page faults of a pager
object, the pager activation dissolves the corresponding signal context from
its signal receiver. If a thread wants to start communicating its page faults
via a pager object, the thread calls Kernel::route_thread_event with its
thread ID, event ID "FAULT", and the invalid signal context ID.
Remove Kernel::resume_faulter.
Move all page fault related code from generic kernel sources to CPU
specific cpu_support.h and cpu_support.cc.
fix#935
