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_0_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1f35170395b79224cda272ba97572b515d57f0d8

Modified Files
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src/interfaces/libpq/fe-connect.c |  187 +++++++++++++++++++++++++------------
1 file changed, 129 insertions(+), 58 deletions(-)