Previously we needed to include headers required by the various
sudo*h files. Now those files are more self-sufficient and we
should only include headers needed by code in the various .c files.
o The parse tree is now passed to the alias, match and defaults functions.
o The nss API has been changed so that the nss parse() function returns
a pointer to a struct sudoers_parse_tree which will be filled in
by the getdefs() and query() functions.
in a per-nss list of userspecs and defaults instead of using separate
lookup and list functions. This makes it possible to have a single
implementation of the code for sudoers lookup and listing.
