pgsql: When executing a list of queries derived from rule expansion,

Log Message:
-----------
When executing a list of queries derived from rule expansion,
_SPI_execute_plan's return code should reflect the type of the query
that is marked canSetTag, not necessarily the last one in the list.

This is arguably a bug fix, but I'm hesitant to back-patch it because
it's the sort of subtle change that might break someone's code, and it's
best not to do that kind of thing in point releases.

Modified Files:
--------------
    pgsql/src/backend/executor:
        spi.c (r1.155 -> r1.156)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/spi.c.diff?r1=1.155&r2=1.156)