Extension switches: -fexistentials

[Ralf Hinze]

GHC supports dozens of type system extensions, which is great.
However, many of them come with their own syntax, which makes
separate switches hard to implement. One relatively mild
extension is support for existential types. Now, if we adopt the
debatable and debated convention that local type variables on
the rhs of type declarations are implicitly existentially
quantified, then this particular extension does not need any
new syntax. Which in turn might make a separate switch such as
	-fexistentials
relatively easy to implement?

Cheers, Ralf