kernel_debugger() didn't do enough before; panic() did all the work - but
since the former is a public function as well, I moved all the functionality
to it. Also fixed a possible buffer overrun in panic().
Renamed dbg_* to debug_*.
"serial_debug_port" setting did not ignore negative values.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12889 a95241bf-73f2-0310-859d-f6bbb57e9c96