pgsql: Improvements to the CREATE DATABASE reference page's description

Log Message:
-----------
Improvements to the CREATE DATABASE reference page's description of the
TABLESPACE clause.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
create_database.sgml (r1.42 -> r1.43)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_database.sgml.diff?r1=1.42&r2=1.43)