Remove HAVE_POSIX_SIGNALS from config.h

Compiling slony against PG 9.4 gives compiler warnings because the
definition of HAVE_POSIX_SIGNALS has changed.  This is defined in pg_config
so we do not really need to redefine it in the config.h slony provides.

We leave the configure check in place to we just don't include it in
the header
Bug 342 - Fix various failover issues

This commit fixes some related failover issues
1.  The query slonik used to get a node list during failover
    was ignoring non-failover targets. This meant that we
    would never call preFailover on a node that wasn't a failover
    target.  This node might then still be trying to use
    a failed provider.
2.  A node (say node 3) might process a FAILOVER_NODE
    event from node 2 (the new-origin) but might not
    have yet processed the last event from node 1, the
    failed node.  We need to make sure that the
    subscription paths and listen networks are updated
    so we don't only listen for events and data from
    failed nodes.
fixing generate load origin node parameter mismatch
Merge remote-tracking branch 'origin/master' into logical_remote_helper

Conflicts:
	src/backend/slony1_funcs.sql
fix merge error
drop the replication slot when dropping the node
bug 354 fix
keep wal rows in the queue from proviers we aren't listening
on in case we need them later (ie after a failover)