`..` in tuple-like patterns (tracking issue for RFC 1492)

[nikomatsakis]

Tracking issue for rust-lang/rfcs#1492

[petrochenkov]

I'll rebase #32079 this weekend.

[petrochenkov]

I don't see neither anything preventing stabilization of this feature, nor strong motivation to stabilize it immediately.
.. currently works in beta (1.11) and nightly (1.12), I suggest to stabilize it in in 1.13 (the next cycle), unless someone want it sooner or has reservations.