Put some kind of grammatical uniformity in the <refpurpose> lines.

doc/src/sgml/ref/abort.sgml

doc/src/sgml/ref/alter_group.sgml

doc/src/sgml/ref/alter_table.sgml

doc/src/sgml/ref/alter_user.sgml

doc/src/sgml/ref/analyze.sgml

doc/src/sgml/ref/begin.sgml

doc/src/sgml/ref/checkpoint.sgml

doc/src/sgml/ref/close.sgml

doc/src/sgml/ref/cluster.sgml

doc/src/sgml/ref/comment.sgml

doc/src/sgml/ref/commit.sgml

doc/src/sgml/ref/copy.sgml

doc/src/sgml/ref/create_aggregate.sgml

doc/src/sgml/ref/create_constraint.sgml

doc/src/sgml/ref/create_database.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_operator.sgml