small extension to `...` notation

[Ben Rudiak-Gould]

Philippa Cowderoy wrote:
> On Wed, 8 Mar 2006, Doaitse Swierstra wrote:
>>  xs `zipWith (+)` ys
> 
> There is one problem with this: it doesn't nest [...]

Another problem is that it's not clear how to declare the fixity of these 
things. Should they always have the default fixity? Should they be required 
to have the form `<ident> <args>` and use the fixity of `ident`? Neither 
approach seems very clean.

-- Ben