pgsql: Fix pg_hba.conf matching so that replication connections only

Log Message:
-----------
Fix pg_hba.conf matching so that replication connections only match records
with database = replication. The previous coding would allow them to match
ordinary records too, but that seems like a recipe for security breaches.
Improve the messages associated with no-such-pg_hba.conf entry to report
replication connections as such, since that's now a critical aspect of
whether the connection matches. Make some cursory improvements in the related
documentation, too.

Modified Files:
--------------
pgsql/doc/src/sgml:
client-auth.sgml (r1.136 -> r1.137)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/client-auth.sgml?r1=1.136&r2=1.137)
high-availability.sgml (r1.61 -> r1.62)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/high-availability.sgml?r1=1.61&r2=1.62)
recovery-config.sgml (r2.4 -> r2.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/recovery-config.sgml?r1=2.4&r2=2.5)
pgsql/src/backend/libpq:
auth.c (r1.199 -> r1.200)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c?r1=1.199&r2=1.200)
hba.c (r1.205 -> r1.206)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c?r1=1.205&r2=1.206)
pgsql/src/backend/replication/libpqwalreceiver:
libpqwalreceiver.c (r1.9 -> r1.10)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c?r1=1.9&r2=1.10)