swift234

Allow a variadic parameter anywhere in the parameter list.

Requiring a variadic parameter to come at the end of the parameter
list is an old restriction that makes no sense nowadays, and which we
had all thought we had already lifted. It made variadic parameters
unusable with trailing closures or defaulted arguments, and made our
new print() design unimplementable.

Remove this restriction, replacing it with a less onerous and slightly
less silly restriction that we not have more than one variadic
parameter in a given parameter clause. Fixes rdar://problem/20127197.

Swift SVN r30542