- use a get_hooktab() function to determine the hook table.
- PROCESS_HOOK now jumps to a cleanup tag on failure
- add PROCESS_ALL_HOOKS in query.c, to run all hook functions at
  a specified hook point without stopping. this is to be used for
  intiialization and destruction functions that must run in every
  module.
- 'result' is set in PROCESS_HOOK only when a hook function
  interrupts processing.
- revised terminology: a "callback" is now a "hook action"
- remove unused NS_PROCESS_HOOK and NS_PROCESS_HOOK_VOID macros.