Fixed some warnings from clang

src/impl/unix.cc

@@ -88,7 +88,6 @@ Serial::SerialImpl::open ()
       case ENFILE:
       case EMFILE:
         THROW (IOException, "Too many file handles open.");
-        break;
       default:
         THROW (IOException, errno);
     }

src/serial.cc

@@ -152,6 +152,7 @@ Serial::readline (string &buffer, size_t size, string eol)
       break; // Reached the maximum read length
     }
   }
+  buffer.append(reinterpret_cast<const char*> (buffer_), read_so_far);
   return read_so_far;
 }