Pageant and PuTTYgen About boxes: add the website button.

While I'm looking at these two dialog boxes, I notice there's another
prominent difference between PuTTY's one and these: I also never got
round to adding the button to go to PuTTY's main website. Now added.

windows/winpgnt.c

@@ -175,6 +175,12 @@ static INT_PTR CALLBACK AboutProc(HWND hwnd, UINT msg,
 	    EnableWindow(hwnd, 1);
 	    SetActiveWindow(hwnd);
 	    return 0;
+	  case 102:
+	    /* Load web browser */
+	    ShellExecute(hwnd, "open",
+			 "http://www.chiark.greenend.org.uk/~sgtatham/putty/",
+			 0, 0, SW_SHOWDEFAULT);
+	    return 0;
 	}
 	return 0;
       case WM_CLOSE: