Proposal: Remove references to guava library from public APIs

There was a good discussion on the mailing list: http://curator.markmail.org/thread/yjete2ozm32jmz5u

The critical portion copied here:

The problem classes that I have found are:

• curator-framework: org.apache.curator.framework.listen.ListenerContainer : method forEach takes a parameter of type com.google.common.base.Function
• curator-framework: org.apache.curator.framework.api.transaction.CuratorTransactionResult : method ofTypeAndPath returns com.google.common.base.Predicate
• curator-x-discovery-server: org.apache.curator.x.discovery.server.contexts.GenericDiscoveryContext : constructor takes param of type com.google.common.reflect.TypeToken
• curator-x-discovery: org.apache.curator.x.discovery.InstanceFilter : inherits from com.google.common.base.Predicate

In the ensuing discussion, it sounded like we'd need to get started on an implementation before we had enough information to determine whether the changes are too intrusive or not.