psql: allow DROP INDEX CONCURRENTLY in AUTOCOMMIT off mode

Previously this threw an error.

Patch by Feike Steenbergen

src/bin/psql/common.c

@@ -1643,6 +1643,24 @@ command_no_begin(const char *query)
 			return true;
 		if (wordlen == 10 && pg_strncasecmp(query, "tablespace", 10) == 0)
 			return true;
+
+		/* DROP INDEX CONCURRENTLY isn't allowed in xacts */
+		if (wordlen == 5 && pg_strncasecmp(query, "index", 5) == 0)
+		{
+			query += wordlen;
+
+			query = skip_white_space(query);
+
+			wordlen = 0;
+			while (isalpha((unsigned char) query[wordlen]))
+				wordlen += PQmblen(&query[wordlen], pset.encoding);
+
+			if (wordlen == 12 && pg_strncasecmp(query, "concurrently", 12) == 0)
+				return true;
+
+			return false;
+		}
+
 		return false;
 	}