pgsql: Docs: fix incorrect spelling of contrib/pgcrypto option.

Docs: fix incorrect spelling of contrib/pgcrypto option.

pgp_sym_encrypt's option is spelled "sess-key", not "enable-session-key".
Spotted by Jeff Janes.

In passing, improve a comment in pgp-pgsql.c to make it clearer that
the debugging options are intentionally undocumented.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/65b0de44f54653021ebec9ad0bb7d60fcb50ff75

Modified Files
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contrib/pgcrypto/pgp-pgsql.c |    5 ++++-
doc/src/sgml/pgcrypto.sgml   |    4 ++--
2 files changed, 6 insertions(+), 3 deletions(-)