added show_in_pager hook

Shell command bug corrected thanks to new shell_cmd hook.

%tasks shows elapsed time in min:sec

added %tasks and %kill to jobctrl, as a powerful way to kill stalling foreground tasks (and ctrl+C won't cut it)

added 'shell_hook' for hooking own 'system()' implementations

.pyw support for %run completer

check for set (python 2.3 compatibility). Closes #209

Removed hotshot profiler!

added a "warning experimental work" at startup

'magic' command handling