bootstrap: support for 'in' collection operator

Does not yet support this form:

	x in {1 2 3}

Indeed, a slice is not a Collection, as t is not `Has_equality.

We would have to constraint the RHS with some kind of `__literal_set__.

In the meantime, this can work:

	x in {1 2 3}:(Hashset Uint)
Accept recent test output changes
bootstrap:autointf: add `Enum and `Union earlier in passfwd
bootstrap:lexer: fix priority of TPOSTQMARK

Was clearly bogus when parsing 'x.y?'