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.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=slony1-engine.git;a=commitdiff;h=f97ef5aed23b031da586ef6e46f9875c5d99b005

Modified Files
--------------
src/backend/slony1_funcs.sql |   52 ++++++++++++++++++++++++++++++++++--------
src/slonik/slonik.c          |   44 ++++++++++++++++++++++++++---------
2 files changed, 75 insertions(+), 21 deletions(-)