Refuse snapshots during bootstrap.
Patch by brandonwilliams, reviewed by thobbs for CASSANDRA-6585
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/service/StorageService.java
Initial pass at deferring the release of new sttables until a stream session is complete. CASSANDRA-6503
split FileMessage into two: IncomingFileMessage and OutgoingFileMessage. Also extended StreamMessage.Type
to have both an incoming message serializer and deserializer; needed this to support Type.File having two diff serializers
as java generics would not let me return different subclasses (of FileMessage) from the original FM.Serializer. Hence, needed to
brea it into two serializers, and thus extend SM.Type.
aborting the SSTW when the session closes with a failure state
adding support for streaming lockfiles, created after streaming is done but before
converting the SSTW to SSTR (and removing the lockfile after we're done).