Problem: trying to repair an old (e.g. with "old" varstring fields) corrupted 
table with use_frm option we don't actually repair the table, just altering it
which may couse data loss.

Fix: if use_frm repair option is set, do repair instead of altering even 
if the table needs upgrade.


sql/sql_table.cc:
  Fix for bug #29980: 5.1.20 ate my table