pgsql: Add configuration parameter ssl_renegotiation_limit to control

Log Message:
-----------
Add configuration parameter ssl_renegotiation_limit to control
how often we do SSL session key renegotiation. Can be set to
0 to disable renegotiation completely, which is required if
a broken SSL library is used (broken patches to CVE-2009-3555
a known cause) or when using a client library that can't do
renegotiation.

Tags:
----
REL8_3_STABLE

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.164.2.6 -> r1.164.2.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.164.2.6&r2=1.164.2.7)
    pgsql/src/backend/libpq:
        be-secure.c (r1.83.2.3 -> r1.83.2.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/be-secure.c?r1=1.83.2.3&r2=1.83.2.4)
    pgsql/src/backend/utils/misc:
        guc.c (r1.432.2.6 -> r1.432.2.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.432.2.6&r2=1.432.2.7)
        postgresql.conf.sample (r1.236 -> r1.236.2.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.236&r2=1.236.2.1)