[Dev] semantic tests during cost parsing

[jbcaillau]

@ocots the semantic test below, currently done in onepass.jl during the (syntaxic) pattern matching, should be deferred to p_lagrange!. i'm changing it unless you remember why you or me put it here. same thing for other kinds of costs.

NB. no need to make a fix in CTBase, i'm updating it directly in CTParser.onepass

        # lagrange cost
        :(∫($e1) → min) => p_lagrange!(p, ocp, e1, :min; log)
        :(-∫($e1) → min) => p_lagrange!(p, ocp, :(-$e1), :min; log)
        :($e1 * ∫($e2) → min) => if has(e1, p.t)
            (return __throw("time $(p.t) must not appear in $e1", p.lnum, p.line))