Node-depend binaries and pg_upgrade support

[AndrewBille]

For example:
node_old = get_new_node(prefix='/path/to/old/pg/prefix')
node_old.init()
node_new=get_new_node(prefix='/path/to/new/pg/prefix')
node_new.init()
node_new.upgade_from(old=node_old)

[demonolock]

Will be done in the next release 1.10.0