psql: Rename results to result when only a single one is meant

This makes the naming more consistent with the libpq API and the rest
of the code, and makes actually supporting multiple result sets in the
future less confusing.

Discussion: https://www.postgresql.org/message-id/flat/db72fb98-9b43-d776-7247-6ed38f28e7c6%40enterprisedb.com

Author: petere

src/bin/psql/command.c

@@ -279,7 +279,7 @@ HandleSlashCmds(PsqlScanState scan_state,
  * Subroutine to actually try to execute a backslash command.
  *
  * The typical "success" result code is PSQL_CMD_SKIP_LINE, although some
- * commands return something else.  Failure results are PSQL_CMD_ERROR,
+ * commands return something else.  Failure result code is PSQL_CMD_ERROR,
  * unless PSQL_CMD_UNKNOWN is more appropriate.
  */
 static backslashResult
@@ -683,7 +683,7 @@ exec_command_copyright(PsqlScanState scan_state, bool active_branch)
 }
 
 /*
- * \crosstabview -- execute a query and display results in crosstab
+ * \crosstabview -- execute a query and display result in crosstab
  */
 static backslashResult
 exec_command_crosstabview(PsqlScanState scan_state, bool active_branch)
@@ -5084,7 +5084,7 @@ do_watch(PQExpBuffer query_buf, double sleep)
 					 timebuf, sleep);
 		myopt.title = title;
 
-		/* Run the query and print out the results */
+		/* Run the query and print out the result */
 		res = PSQLexecWatch(query_buf->data, &myopt, pagerpipe);
 
 		/*