NO... dsdb-extended: use a cache of dsdb_attributes for the current request

NO... dsdb-extended: use a cache of dsdb_attributes for the current request

The logic is that for a given search it's often the same given search of
attributes in the same order that is used, so we use a small cache
instead of doing a binary search in the attributes_by_ldapname of the
schema. It helps to reduce the time spent doing strcasecmp.

NO: if we use a cache then it should be global and hidden inside of
dsdb_attribute_by_lDAPDisplayName() in order to speed of all modules.