Add function name to errors raised by PQsend...

These functions don't emit an error by PQerrorMessage() so far.
To make the error more useful, this adds at least the failing function as error message.

ext/pg_connection.c

@@ -1947,7 +1947,7 @@ pgconn_send_query(int argc, VALUE *argv, VALUE self)
 	/* If called with no or nil parameters, use PQexec for compatibility */
 	if ( argc == 1 || (argc >= 2 && argc <= 4 && NIL_P(argv[1]) )) {
 		if(gvl_PQsendQuery(this->pgconn, pg_cstr_enc(argv[0], this->enc_idx)) == 0)
-			pg_raise_conn_error( rb_eUnableToSend, self, "%s", PQerrorMessage(this->pgconn));
+			pg_raise_conn_error( rb_eUnableToSend, self, "PQsendQuery %s", PQerrorMessage(this->pgconn));
 
 		pgconn_wait_for_flush( self );
 		return Qnil;
@@ -2022,7 +2022,7 @@ pgconn_send_query_params(int argc, VALUE *argv, VALUE self)
 	free_query_params( &paramsData );
 
 	if(result == 0)
-		pg_raise_conn_error( rb_eUnableToSend, self, "%s", PQerrorMessage(this->pgconn));
+		pg_raise_conn_error( rb_eUnableToSend, self, "PQsendQueryParams %s", PQerrorMessage(this->pgconn));
 
 	pgconn_wait_for_flush( self );
 	return Qnil;
@@ -2083,7 +2083,7 @@ pgconn_send_prepare(int argc, VALUE *argv, VALUE self)
 	xfree(paramTypes);
 
 	if(result == 0) {
-		pg_raise_conn_error( rb_eUnableToSend, self, "%s", PQerrorMessage(this->pgconn));
+		pg_raise_conn_error( rb_eUnableToSend, self, "PQsendPrepare %s", PQerrorMessage(this->pgconn));
 	}
 	pgconn_wait_for_flush( self );
 	return Qnil;
@@ -2149,7 +2149,7 @@ pgconn_send_query_prepared(int argc, VALUE *argv, VALUE self)
 	free_query_params( &paramsData );
 
 	if(result == 0)
-		pg_raise_conn_error( rb_eUnableToSend, self, "%s", PQerrorMessage(this->pgconn));
+		pg_raise_conn_error( rb_eUnableToSend, self, "PQsendQueryPrepared %s", PQerrorMessage(this->pgconn));
 
 	pgconn_wait_for_flush( self );
 	return Qnil;
@@ -2168,7 +2168,7 @@ pgconn_send_describe_prepared(VALUE self, VALUE stmt_name)
 	t_pg_connection *this = pg_get_connection_safe( self );
 	/* returns 0 on failure */
 	if(gvl_PQsendDescribePrepared(this->pgconn, pg_cstr_enc(stmt_name, this->enc_idx)) == 0)
-		pg_raise_conn_error( rb_eUnableToSend, self, "%s", PQerrorMessage(this->pgconn));
+		pg_raise_conn_error( rb_eUnableToSend, self, "PQsendDescribePrepared %s", PQerrorMessage(this->pgconn));
 
 	pgconn_wait_for_flush( self );
 	return Qnil;