convert coherence-cow to use revisions

Author: nikomatsakis

src/test/compile-fail/coherence-cow-2.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// revisions: a b c
+
 // aux-build:coherence_lib.rs
 
 // pretty-expanded FIXME #23616
@@ -22,7 +24,14 @@ use lib::{Remote,Pair};
 
 pub struct Cover<T>(T);
 
-impl<T> Remote for Pair<T,Cover<T>> { }
-//~^ ERROR E0210
+#[cfg(a)]
+impl<T> Remote for Pair<T,Cover<T>> { } //[a]~ ERROR E0210
+
+#[cfg(b)]
+impl<T> Remote for Pair<Cover<T>,T> { } //[b]~ ERROR E0210
+
+#[cfg(c)]
+impl<T,U> Remote for Pair<Cover<T>,U> { }
+//[c]~^ ERROR type parameter `T` must be used as the type parameter for some local type
 
 fn main() { }