pgsql: Refactor libpq authentication request processing.

Refactor libpq authentication request processing.

Move the responsibility of reading the data from the authentication request
message from PQconnectPoll() to pg_fe_sendauth(). This way, PQconnectPoll()
doesn't need to know about all the different authentication request types,
and we don't need the extra fields in the pg_conn struct to pass the data
from PQconnectPoll() to pg_fe_sendauth() anymore.

Reviewed by Michael Paquier.

Discussion: https://www.postgresql.org/message-id/6490b975-5ee1-6280-ac1d-af975b19fb9a%40iki.fi

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/61bf96cab06390fec66405d3caad789f4417f25a

Modified Files
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src/interfaces/libpq/fe-auth.c | 230 ++++++++++++++++++++++++++++----------
src/interfaces/libpq/fe-auth.h | 2 +-
src/interfaces/libpq/fe-connect.c | 129 +++++----------------
src/interfaces/libpq/libpq-int.h | 11 +-
4 files changed, 202 insertions(+), 170 deletions(-)