[PATCH] add 'concat! : List % -> %' in URAGG

[oldk1331]

We already have 'concat : List % -> %', and it's equally
useful to have its destructive counterpart, for long lists,
this version can save many many copies.

Although 'concat : List % -> %' is exported in LNAGG,
I believe that the proper place for
'concat/concat! : List % -> %' should be in URAGG.

[oldk1331]

There's a bug: it gives error when the first aggregate
in the list is empty, see my updated version.

[Waldek Hebisch]

oldk1331 wrote:
>
> There's a bug: it gives error when the first aggregate
> in the list is empty, see my updated version.

OK, please commit

--
Waldek Hebisch