for getting the list of variable names and for clearing all rule and
variable storage.
* compile.c - better error reporting for unknown rules; now it is a
hard error.
* hash.c/h - added hash_free to allow removal of elements from a hash
* rule.c/h - implemented rule freeing; stopped exporting rules to the
global module by default.
* variable.c - reclaim variable storage when disposing of variable
hash.
* build.jam - make grammar building work under NT
[SVN r18405]