pgsql: libpq: Allow connection strings and URIs to specify multiple hos

pgsql: libpq: Allow connection strings and URIs to specify multiple hos

libpq: Allow connection strings and URIs to specify multiple hosts.

It's also possible to specify a separate port for each host.

Previously, we'd loop over every address returned by looking up the
host name; now, we'll try every address for every host name.

Patch by me.  Victor Wagner wrote an earlier patch for this feature,
which I read, but I didn't use any of his code.  Review by Mithun Cy.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/274bb2b3857cc987cfa21d14775cae9b0dababa5

Modified Files
--------------
doc/src/sgml/libpq.sgml           |  38 ++-
src/interfaces/libpq/fe-auth.c    |  28 +-
src/interfaces/libpq/fe-connect.c | 607 ++++++++++++++++++++++++++------------
src/interfaces/libpq/libpq-int.h  |  41 ++-
4 files changed, 506 insertions(+), 208 deletions(-)