When it is known that there is already at least one element in the
list, it is awkwardly verbose to use three lines and an extra
variable declaration to remove the first or last item (a common
case), rather than use a simple expression.

a stack:
	stk.PushFront(x)
	x = stk.Front().Remove().(T)

vs.
	stk.PushFront(x)
	e := stk.Front()
	e.Remove()
	x = e.Value.(T)
[An alternative CL might be to add PopFront and PopBack methods].

R=gri
CC=golang-dev
https://golang.org/cl/3000041