More editing of reference pages.

doc/src/sgml/ref/create_aggregate.sgml

doc/src/sgml/ref/create_cast.sgml

doc/src/sgml/ref/create_constraint.sgml

doc/src/sgml/ref/create_conversion.sgml

doc/src/sgml/ref/create_database.sgml

doc/src/sgml/ref/create_domain.sgml

doc/src/sgml/ref/create_function.sgml

doc/src/sgml/ref/create_group.sgml

doc/src/sgml/ref/create_index.sgml

doc/src/sgml/ref/create_language.sgml

doc/src/sgml/ref/create_opclass.sgml

doc/src/sgml/ref/create_operator.sgml

doc/src/sgml/ref/create_rule.sgml

doc/src/sgml/ref/create_schema.sgml

doc/src/sgml/ref/create_sequence.sgml

doc/src/sgml/ref/create_table.sgml

doc/src/sgml/ref/create_table_as.sgml

doc/src/sgml/ref/create_trigger.sgml

doc/src/sgml/ref/create_type.sgml

doc/src/sgml/ref/create_user.sgml