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.

Modified Files:
--------------
    pgsql/src/backend/main:
        main.c (r1.99 -> r1.100)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/main/main.c.diff?r1=1.99&r2=1.100)
    pgsql/src/backend/postmaster:
        postmaster.c (r1.479 -> r1.480)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c.diff?r1=1.479&r2=1.480)
    pgsql/src/include/postmaster:
        postmaster.h (r1.11 -> r1.12)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/postmaster/postmaster.h.diff?r1=1.11&r2=1.12)
    pgsql/src/port:
        path.c (r1.63 -> r1.64)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/path.c.diff?r1=1.63&r2=1.64)