pgsql: The proper guaranteed buffer size for errors is

Log Message:
-----------
The proper guaranteed buffer size for errors is
INITIAL_EXPBUFFER_SIZE, not PQERRORMSG_LENGTH.

Backport only - the proper fix in HEAD is to
use PQExpBuffers everywhere.

Tags:
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REL7_4_STABLE

Modified Files:
--------------
pgsql/src/interfaces/libpq:
fe-auth.c (r1.84.2.3 -> r1.84.2.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c.diff?r1=1.84.2.3&r2=1.84.2.4)
fe-connect.c (r1.263.2.5 -> r1.263.2.6)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c.diff?r1=1.263.2.5&r2=1.263.2.6)
libpq-int.h (r1.82.2.2 -> r1.82.2.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h.diff?r1=1.82.2.2&r2=1.82.2.3)