patch 8.2.0774: t_TI and t_TE are output when using 'visualbell'

Problem:    t_TI and t_TE are output when using 'visualbell'. (Dominique
            Pelle)
Solution:   Do not change the terminal mode for a short sleep.  Do not output
            t_TI and t_TE when switching to/from TMODE_SLEEP. Make tmode an
            enum.
diff --git a/src/os_amiga.c b/src/os_amiga.c
index 58e462d..850c26a 100644
--- a/src/os_amiga.c
+++ b/src/os_amiga.c
@@ -977,7 +977,7 @@
  *	it sends a 0 to the console to make it back into a CON: from a RAW:
  */
     void
-mch_settmode(int tmode)
+mch_settmode(tmode_T tmode)
 {
 #if defined(__AROS__) || defined(__amigaos4__)
     if (!SetMode(raw_in, tmode == TMODE_RAW ? 1 : 0))