sort *all* GetSignBytes:

- call MustSortJSON before return JSON bytes to guarantee alphabetic
ordering

- moved SortJSON and MustSortJSON to types package to avoid cyclic
package dep

docs/core/examples/app1.go

@@ -85,7 +85,7 @@ func (msg MsgSend) GetSignBytes() []byte {
 	if err != nil {
 		panic(err)
 	}
-	return bz
+	return sdk.MustSortJSON(bz)
 }
 
 // Implements Msg. Return the signer.

docs/core/examples/app2.go

@@ -100,7 +100,7 @@ func (msg MsgIssue) GetSignBytes() []byte {
 	if err != nil {
 		panic(err)
 	}
-	return bz
+	return sdk.MustSortJSON(bz)
 }
 
 // Implements Msg. Return the signer.