Fix for log_executor_stats

The log_executor_stats config variable doesn't work 100%. It shows
stats for only certain SQL queries. Looking at utils/portal.h:

* We have several execution strategies for Portals, depending on what
* query or queries are to be executed. (Note: in all cases, a Portal
* executes just a single source-SQL query, and thus produces just a
* single result from the user's viewpoint. However, the rule rewriter
* may expand the single source query to zero or many actual queries.)
*
* PORTAL_ONE_SELECT: the portal contains one single SELECT query. We run
* the Executor incrementally as results are demanded. This strategy also
* supports holdable cursors (the Executor results can be dumped into a
* tuplestore for access after transaction completion).
*
* PORTAL_UTIL_SELECT: the portal contains a utility statement that returns
* a SELECT-like result (for example, EXPLAIN or SHOW). On first execution,
* we run the statement and dump its results into the portal tuplestore;
* the results are then returned to the client as demanded.
*
* PORTAL_MULTI_QUERY: all other cases. Here, we do not support partial
* execution: the portal's queries will be run to completion on first call.

it only logs executor stats for PORTAL_MULTI_QUERY queries. I assume
this was done so that individual queries are logged rather than the
entire multi-query. However, the code shows no executor stats for
non-multi queries, which is certainly a bug. Even a simple "SELECT col
FROM tab" or "SELECT 1" emits no statistics.

This used to work in the past, but it appears broken in 7.4.X too. I
guess I should fix it there too, though obviously very few people use
this feature or we would have gotten reports.

The attached fix keeps the multi-query stats code unchanged, but adds
stats for non-multi-query cases.

--
Bruce Momjian | http://candle.pha.pa.us
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