This patch adds a vector for debug events along with a hook similar to
the exception framework. The debug vector generates an exception frame
for use by libdebugger.
This patch updates the CPU_Exception_frame to include all necessary
registers, combines hardware snd software exception handlers into a
shared vector, provides an architecture-specific hook for taking
control of exception handling, and moves exception handling over to
actually using the CPU_Exception_frame instead of a minimal interrupt
stack frame. As the significant contents of _exception_handler.S have
been entirely rewritten, the copyright information on this file has been
updated to reflect that.
