List concatenation

[Charles]

I've added support for "a + b" for lists.

a = [1, 2]
b = [3, 4]
assert a + b == [1, 2, 3, 4]

This will work for anything IList<of T>. The two operands are left unmodified and a new list instance is created using a's type.

Haven't gotten to "a += b" yet.

[Charles]

"a += b" works now.