pgsql: Rename the parameter recovery_connections to hot_standby, to

Log Message:
-----------
Rename the parameter recovery_connections to hot_standby, to reduce possible
confusion with streaming-replication settings.  Also, change its default
value to "off", because of concern about executing new and poorly-tested
code during ordinary non-replicating operation.  Per discussion.

In passing do some minor editing of related documentation.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.271 -> r1.272)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.271&r2=1.272)
        high-availability.sgml (r1.64 -> r1.65)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/high-availability.sgml?r1=1.64&r2=1.65)
    pgsql/src/backend/access/transam:
        xlog.c (r1.405 -> r1.406)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.405&r2=1.406)
    pgsql/src/backend/storage/ipc:
        procarray.c (r1.67 -> r1.68)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/procarray.c?r1=1.67&r2=1.68)
    pgsql/src/backend/utils/misc:
        guc.c (r1.552 -> r1.553)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.552&r2=1.553)
        postgresql.conf.sample (r1.285 -> r1.286)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.285&r2=1.286)
    pgsql/src/include/access:
        xlog.h (r1.110 -> r1.111)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xlog.h?r1=1.110&r2=1.111)