Re: MERGE ... RETURNING

Hi, some minor issues:

<synopsis>
[ WITH <replaceable class="parameter">with_query</replaceable> [, ...] ]
MERGE INTO [ ONLY ] <replaceable
class="parameter">target_table_name</replaceable> [ * ] [ [ AS ]
<replaceable class="parameter">target_alias</replaceable> ]
USING <replaceable class="parameter">data_source</replaceable> ON
<replaceable class="parameter">join_condition</replaceable>
<replaceable class="parameter">when_clause</replaceable> [...]
[ RETURNING * | <replaceable
class="parameter">output_expression</replaceable> [ [ AS ]
<replaceable class="parameter">output_name</replaceable> ] [, ...] ]

here the "WITH" part should have "[ RECURSIVE ]" like:
[ WITH [ RECURSIVE ] <replaceable
class="parameter">with_query</replaceable> [, ...] ]

+ An expression to be computed and returned by the <command>MERGE</command>
+ command after each row is merged. The expression can use any columns of
+ the source or target tables, or the <xref linkend="merge_action"/>
+ function to return additional information about the action executed.
+ </para>
should be:
+ An expression to be computed and returned by the <command>MERGE</command>
+ command after each row is changed.

one minor issue:
add
`
table sq_target;
table sq_source;
`
before `-- RETURNING` in src/test/regress/sql/merge.sql, so we can
easily understand the tests.