pgsql: Check return value of strdup() in libpq connection option parsin

Check return value of strdup() in libpq connection option parsing.

An out-of-memory in most of these would lead to strange behavior, like
connecting to a different database than intended, but some would lead to
an outright segfault.

Alex Shulgin and me. Backpatch to all supported versions.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/abcab2a64fb050e9ff8f4a3d9b51122c6d7baecd

Modified Files
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src/interfaces/libpq/fe-connect.c |  218 +++++++++++++++++++++++++------------
1 file changed, 148 insertions(+), 70 deletions(-)