SI-8451 makes uncurry more forgiving

At the moment uncurry expects that all constructors must have blocks
as their bodies. This is generally true, because that's how parser and typer
work at the moment, but why impose more preconditions than necessary?
This commit allows arbitrary expressions as well.
SI-8451 quasiquotes now handle quirks of secondary constructors

Apparently even though the rhs of a secondary constructor looks like an expr,
it always gets wrapped in a block by the parser. This works just fine with
the typer, but crashes in uncurry. The parent commit fixes the situation
with uncurry, and this one brings quasiquotes in line with the parser.