Handle schema reloading request.

Handle schema reloading request.
The ldif for that operation looks like this:

dn:
changetype: Modify
add: schemaUpdateNow
schemaUpdateNow: 1

It uses the rootdse's object functional attribute schemaUpdateNow.
In rootdse_modify() this command is being recognized and it is send as extended operation with DSDB_EXTENDED_SCHEMA_UPDATE_NOW_OID.
In the partition module its dispatched to the schema_fsmo module.
The request is processed in the schema_fsmo module by schema_fsmo_extended().
(This used to be commit 39f9184ddf215f2b512319211c0a05702218ef87)