Hacky test implementation to perform local broadcaster reads. Needs lots of cleanup.
Previous test version performed the read twice.
Merge branch 'next' into daniel_1886_local

Conflicts:
	src/clustering/immediate_consistency/branch/listener.cc
Completed the local operation interface in listener_t.
Things
Made direct listener operations interruptible, + some cleanup.
== NULL should have been != NULL
Simplified and improved keepalive management for the local listener.
Merge branch 'next' into daniel_1886_local
Merge branch 'next' into daniel_1886_local

Conflicts:
	src/clustering/immediate_consistency/branch/broadcaster.cc
	src/clustering/immediate_consistency/branch/metadata.hpp