Adjust error message for method type mismatch

Closes #10118, Closes #5925

Author: emberian

src/librustc/middle/typeck/check/mod.rs

@@ -864,7 +864,7 @@ pub fn compare_impl_method(tcx: ty::ctxt,
         tcx.sess.span_err(
             impl_m_span,
             format!("method `{}` has {} parameter{} \
-                  but the trait method `{}` has {}",
+                  but the declaration in trait `{}` has {}",
                  tcx.sess.str_of(trait_m.ident),
                  impl_m.fty.sig.inputs.len(),
                  if impl_m.fty.sig.inputs.len() == 1 { "" } else { "s" },

src/test/compile-fail/trait-impl-different-num-params.rs

@@ -13,7 +13,7 @@ trait foo {
 }
 impl foo for int {
     fn bar(&self) -> int {
-        //~^ ERROR method `bar` has 0 parameters but the trait method `foo::bar` has 1
+        //~^ ERROR method `bar` has 0 parameters but the declaration in trait `foo::bar` has 1
         *self
     }
 }