pgsql: Set progname early in the postmaster/postgres binary, rather than

Log Message:
-----------
Set progname early in the postmaster/postgres binary, rather than doing
it later.  This fixes a problem where EXEC_BACKEND didn't have progname
set, causing a segfault if log_min_messages was set below debug2 and our
own snprintf.c was being used.

Also alway strdup() progname.

Backpatch to 8.1.X and 8.0.X.

Tags:
----
REL8_0_STABLE

Modified Files:
--------------
    pgsql/src/backend/main:
        main.c (r1.94.4.1 -> r1.94.4.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/main/main.c.diff?r1=1.94.4.1&r2=1.94.4.2)
    pgsql/src/backend/postmaster:
        postmaster.c (r1.443.4.5 -> r1.443.4.6)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c.diff?r1=1.443.4.5&r2=1.443.4.6)
    pgsql/src/include/postmaster:
        postmaster.h (r1.9 -> r1.9.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/postmaster/postmaster.h.diff?r1=1.9&r2=1.9.4.1)
    pgsql/src/port:
        path.c (r1.50.4.2 -> r1.50.4.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/path.c.diff?r1=1.50.4.2&r2=1.50.4.3)