[MASSMAIL]pgsql: Refactor libpq state machine for negotiating encryption

Refactor libpq state machine for negotiating encryption

This fixes the few corner cases noted in commit 705843d294, as shown
by the changes in the test.

Author: Heikki Linnakangas, Matthias van de Meent
Reviewed-by: Jacob Champion

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/05fd30c0e730bd5238f62d2fdfdcfaf28b16b225

Modified Files
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src/interfaces/libpq/fe-connect.c                  | 427 ++++++++++++---------
src/interfaces/libpq/libpq-int.h                   |  14 +-
.../libpq_encryption/t/001_negotiate_encryption.pl |  26 +-
3 files changed, 265 insertions(+), 202 deletions(-)