Fix infinite recursion in the compiler.

This was detected by the unconditional_recursion lint.

src/librustc/util/ppaux.rs

@@ -544,7 +544,7 @@ fn repr(&self, tcx: &ctxt<'tcx>) -> String {
 
 impl<'tcx, T:Repr<'tcx>> Repr<'tcx> for P<T> {
     fn repr(&self, tcx: &ctxt<'tcx>) -> String {
-        (*self).repr(tcx)
+        (**self).repr(tcx)
     }
 }