pgsql: Replace strdup() with pstrdup(), to avoid leaking memory.

Replace strdup() with pstrdup(), to avoid leaking memory.

It's been like this since the seg module was introduced, so backpatch to
8.2 which is the oldest supported version.

Branch
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REL8_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/4919a20c3331dbecd170387b58075210d6245f51

Modified Files
--------------
contrib/seg/seg.c |    2 +-
1 files changed, 1 insertions(+), 1 deletions(-)