pgsql-server: Rename the built-in tablespaces to pg_default and

Log Message:
-----------
Rename the built-in tablespaces to pg_default and pg_global, and prohibit
creation of user-defined tablespaces with names starting with 'pg_', as
per suggestion of Chris K-L.  Also install admin-guide tablespace
documentation from Gavin.

Modified Files:
--------------
    pgsql-server/doc/src/sgml:
        diskusage.sgml (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/diskusage.sgml.diff?r1=1.10&r2=1.11)
        manage-ag.sgml (r2.30 -> r2.31)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/manage-ag.sgml.diff?r1=2.30&r2=2.31)
    pgsql-server/doc/src/sgml/ref:
        postmaster.sgml (r1.49 -> r1.50)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/ref/postmaster.sgml.diff?r1=1.49&r2=1.50)
    pgsql-server/src/backend/catalog:
        catalog.c (r1.53 -> r1.54)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/catalog/catalog.c.diff?r1=1.53&r2=1.54)
    pgsql-server/src/backend/commands:
        tablespace.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/tablespace.c.diff?r1=1.2&r2=1.3)
    pgsql-server/src/include/catalog:
        catversion.h (r1.238 -> r1.239)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/catalog/catversion.h.diff?r1=1.238&r2=1.239)
        pg_tablespace.h (r1.1 -> r1.2)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/catalog/pg_tablespace.h.diff?r1=1.1&r2=1.2)