Allow embedding tuples in SR.
Trac #14780: allow embedding python tuples in SR

Attached patch allows embedding Python tuples in symbolic expressions:

{{{
sage: t = SR._force_tuple((1, 2, x, x+1, x+2))
sage: t
(1, 2, x, x + 1, x + 2)
sage: t.subs(x = 2*x^2)
(1, 2, 2*x^2, 2*x^2 + 1, 2*x^2 + 2)
sage: t.op[0]
1
sage: t.op[2]
x
}}}

Apply: [attachment:trac_14780-embed_tuples_in_SR.patch]

URL: http://trac.sagemath.org/14780
Reported by: burcin
Ticket author(s): Burcin Erocal
Reviewer(s): Volker Braun