Bunch of fixes for frames of 2.5 ms.
diff --git a/libcelt/modes.c b/libcelt/modes.c
index b7f9b01..c205db4 100644
--- a/libcelt/modes.c
+++ b/libcelt/modes.c
@@ -339,7 +339,7 @@
    } else if (frame_size >= 320 && (frame_size%8)==0)
    {
      mode->nbShortMdcts = 4;
-   } else if (frame_size >= 120 && (frame_size%4)==0)
+   } else if (frame_size >= 160 && (frame_size%4)==0)
    {
      mode->nbShortMdcts = 2;
    } else