o Made children global so check_exec() can lookup a child.

o Made children global so check_exec() can lookup a child.
o Replaced uid in struct childinfo with struct passwd * (for runas)
o new_child() now takes a parent pid so the runas info can be inherited
o Added find_child() to lookup a child by its pid
o update_child() now fills in a struct passwd
o Converted the big if/else mess in set_policy to a switch
o Syscalls that change uid are now "ask" so we get SYSTR_MSG_UGID events