pgsql: Push enable/disable of notify and catchup interrupts all the way

Log Message:
-----------
Push enable/disable of notify and catchup interrupts all the way down
to just around the bare recv() call that gets a command from the client.
The former placement in PostgresMain was unsafe because the intermediate
processing layers (especially SSL) use facilities such as malloc that are
not necessarily re-entrant.  Per report from counterstorm.com.

Tags:
----
REL7_4_STABLE

Modified Files:
--------------
    pgsql/src/backend/libpq:
        be-secure.c (r1.43.2.1 -> r1.43.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/be-secure.c.diff?r1=1.43.2.1&r2=1.43.2.2)
    pgsql/src/backend/tcop:
        postgres.c (r1.375.2.2 -> r1.375.2.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c.diff?r1=1.375.2.2&r2=1.375.2.3)
    pgsql/src/include/tcop:
        tcopprot.h (r1.60 -> r1.60.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/tcop/tcopprot.h.diff?r1=1.60&r2=1.60.4.1)