add more semantics to the "type" field; fix a bug in anonymous operations; treat children aci_mask() as internal searches

move ACIs under a dynamic infrastructure that allows run-time loadable custom access control logic (needs work)

instead of recycling thru avl_find/avl_delete/avl_insert

using backend-specific locks

add exop_is_write() macro for detecting exops that modify a target entry

select(). If you think this is too ugly, feel free to revert...

(chose 5 arbitrarily)

Deleted broken/unused FD_MANUAL_COPY code