Crash unifying IO and non-IO functions

Actually, this only happens if you also include a pure function with the same signature (sans io). So if you import the prelude, it will crash because of curry2_, but in isolation the above code won't crash. So here is a complete program that exhibits this error:

def curry2_(f :: (a, b) -> r, x :: a) :: b -> r:
    return f(x, ...)
def curryio2_(f :: (a, b) ->io r, x :: a) :: b ->io r:
    return f(x, ...)

Here is an even more minimal example:

def curry0_(f :: () -> r) :: () -> r:
    return f(...)
def curryio0_(f :: () ->io r) :: () ->io r:
    return f(...)

The problem is because the closure template for partially-applying f is being given the same name in both instances: "ct:ty:v1f1:0".

Fixed in trunk r1305.