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.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.252 -> r1.253)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.252&r2=1.253)
    pgsql/src/backend/libpq:
        be-secure.c (r1.97 -> r1.98)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/be-secure.c?r1=1.97&r2=1.98)
    pgsql/src/backend/utils/misc:
        guc.c (r1.541 -> r1.542)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.541&r2=1.542)
        postgresql.conf.sample (r1.277 -> r1.278)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.277&r2=1.278)