Fix [Read|Unread] buttons behaviour

* Allow displaying of "Read" button only for Incoming e-mails.
  Fixes #4773;
* Move to the next message after pressing "Unread" button that
  is consistent with corresponding "Unread" button case.
  Fixes #4774;
* Those problems were fixed during completing GCI 2011 task.

Signed-off-by: Siarzhuk Zharski <[email protected]>

src/apps/mail/MailWindow.cpp

@@ -1478,6 +1478,7 @@ TMailWindow::MessageReceived(BMessage *msg)
 		case M_UNREAD:
 			MarkMessageRead(fRef, B_SEEN);
 			_UpdateReadButton();
+			PostMessage(M_NEXTMSG);
 			break;
 		case M_READ:
 			wasReadMsg = true;
@@ -3190,7 +3191,7 @@ TMailWindow::_UpdateReadButton()
 	if (fApp->ShowButtonBar()) {
 		fButtonBar->RemoveButton(fReadButton);
 		fReadButton = NULL;
-		if (!fAutoMarkRead)
+		if (!fAutoMarkRead && fIncoming)
 			_AddReadButton();
 	}
 	UpdateViews();