ISPN-3976 Protobuf marshalling on Indexed server caches interferes with ...

...keySet and bulk marshalling

This happens only in clustered caches because that's when map-reduce is used to collect the keys and
fails due to ClassCastException. The map-reduce task used to assume the values are byte[] which is no
longer true whith remote query.

Jira: https://issues.jboss.org/browse/ISPN-3976