major upgrade to the ldb attribute handling

major upgrade to the ldb attribute handling

This is all working towards supporting the full WSPP schema without a
major performance penalty.

We now use binary searches when looking up classes and attributes. We
also avoid the loop loading the attributes into ldb, by adding a hook
to override the ldb attribute search function in a module. The
attributes can thus be loaded once, and then saved as part of the
global schema.

Also added support for a few more key attribute syntaxes, as needed
for the full schema.