pgsql: The correct min buffer size is INITIAL_EXPBUFFER_SIZE, not

Log Message:
-----------
The correct min buffer size is
INITIAL_EXPBUFFER_SIZE, not PQERRORMSG_LENGTH.

Backpatch only, the proper fix in HEAD is
to use PQExpBuffers everywhere.

Tags:
----
REL8_1_STABLE

Modified Files:
--------------
    pgsql/src/interfaces/libpq:
        fe-auth.c (r1.107.2.2 -> r1.107.2.3)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-auth.c.diff?r1=1.107.2.2&r2=1.107.2.3)
        fe-connect.c (r1.323.2.2 -> r1.323.2.3)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c.diff?r1=1.323.2.2&r2=1.323.2.3)
        libpq-int.h (r1.108.2.2 -> r1.108.2.3)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h.diff?r1=1.108.2.2&r2=1.108.2.3)