Spec all functions in admin_node_leave.
Spec all functions in admin_partitions.
Add specs for all functions in admin_node_stop.
Spec spec most of the functions in admin_node.
Spec all functions in admin_gui.
spec the remaining functions in admin_cluster_down.
Fix a bunch of warnings generated by dialyzer.
Potentially useful makefile targets for building dialyzer plt files and checking
types.

Mostly taken from riak project.