Relocate schema_init() call to main()

Relocate schema_init() call to main()
Add schema_prep() call to main()
Similiar changes to slapcommon.c
Add schema_prep() impl to schema_init.c
Add slap_ad_entry and slap_ad_children globals.
Add "entry" and "children" to openldap.schema (this likely should
  be added to schema via code, not configuration)