function a_db = plus(left_obj, right_obj)
% plus - Adds a DB to another or to a scalar.
% a_db = plus(left_obj, right_obj)
% If DBs have mismatching columns only the common columns will be kept.
% In any case, the resulting DB columns will be sorted in the order of the
% left-hand-side DB.
% left_obj, right_obj: Operands of the addition. One must be of type tests_db
% and the other can be a scalar or tests_db.
% a_db: The resulting tests_db.
% See also: plus
% Author: Cengiz Gunay <email@example.com>, 2007/12/13
% Copyright (c) 2007 Cengiz Gunay <firstname.lastname@example.org>.
% This work is licensed under the Academic Free License ("AFL")
% v. 3.0. To view a copy of this license, please look at the COPYING
% file distributed with this software or visit
a_db = rop(left_obj, right_obj, @plus, '+');