Make == eq eqv DWIM on Promises

With the emphasis on "I" :-)   Inspired by the first Promises slide in
jnthn++ last presentation:
  http://jnthn.net/papers/2015-yapcasia-concurrency.pdf

It occurred to me that the whole slide could be reduced to:

  sub MAIN($file1, $file2) {
      say (start from-json(slurp($file1)) eqv (start from-json(slurp($file2)))
        ?? 'Files contain identical JSON'
        !! 'Files contain different JSON';
  }

with these changes.

src/core/Promise.pm

@@ -212,6 +212,14 @@ my class Promise {
         });
         $s
     }
+
+    # experimental
+    method Str(Promise:D:)     { self.result.Str     }
+    method Numeric(Promise:D:) { self.result.Numeric }
+}
+
+multi sub infix:<eqv>(Promise:D $a, Promise:D $b) {
+    infix:<eqv>($a.result, $b.result);
 }
 
 # vim: ft=perl6 expandtab sw=4