pgsql-server: Adjust configuration-files GUC behavior as per my recent

Log Message:
-----------
Adjust configuration-files GUC behavior as per my recent proposal.
The vars are renamed to data_directory, config_file, hba_file, and
ident_file, and are guaranteed to be set to accurate absolute paths
during postmaster startup.
This commit does not yet do anything about hiding path values from
non-superusers.

Modified Files:
--------------
    pgsql-server/doc/src/sgml:
        runtime.sgml (r1.286 -> r1.287)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/runtime.sgml.diff?r1=1.286&r2=1.287)
    pgsql-server/src/backend/libpq:
        hba.c (r1.131 -> r1.132)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/libpq/hba.c.diff?r1=1.131&r2=1.132)
    pgsql-server/src/backend/postmaster:
        postmaster.c (r1.430 -> r1.431)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/postmaster/postmaster.c.diff?r1=1.430&r2=1.431)
    pgsql-server/src/backend/utils/init:
        miscinit.c (r1.134 -> r1.135)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/init/miscinit.c.diff?r1=1.134&r2=1.135)
    pgsql-server/src/backend/utils/misc:
        guc.c (r1.240 -> r1.241)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/misc/guc.c.diff?r1=1.240&r2=1.241)
        postgresql.conf.sample (r1.131 -> r1.132)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.131&r2=1.132)
    pgsql-server/src/include:
        miscadmin.h (r1.168 -> r1.169)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/miscadmin.h.diff?r1=1.168&r2=1.169)
    pgsql-server/src/include/utils:
        guc.h (r1.52 -> r1.53)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/utils/guc.h.diff?r1=1.52&r2=1.53)