memory cleanup

["Howard Chu" <hyc@highlandsun.com>]

I've implemented functions to free all the schema structures, not sure if
they're actually useful. I've been looking at a trace of all of slapd's
mallocs and just wanted to eliminate those from the picture while looking
for leaks.
Is it worth checking in? schema_destroy() called from main, which calls
oc_destroy, at_destroy, ad_destroy, mr_destroy, syn_destroy. All of these
are extremely similar functions, avl_free() on the tree etc.

  -- Howard Chu
  Chief Architect, Symas Corp.       Director, Highland Sun
  http://www.symas.com               http://highlandsun.com/hyc
  Symas: Premier OpenSource Development and Support