Additional fix for bug 508023, to make upgrades from 3.1.4 succeed.

Bugzilla/DB/Schema/Mysql.pm

@@ -189,8 +189,10 @@ sub get_alter_column_ddl {
     my %new_defaultless = %$new_def;
     delete $old_defaultless{DEFAULT};
     delete $new_defaultless{DEFAULT};
-    if ($self->columns_equal(\%new_defaultless, \%old_defaultless)) {
-        if (defined $old_def->{DEFAULT} and !defined $new_def->{DEFAULT}) {
+    if (!$self->columns_equal($old_def, $new_def)
+        && $self->columns_equal(\%new_defaultless, \%old_defaultless)) 
+    {
+        if (!defined $new_def->{DEFAULT}) {
             push(@statements,
                  "ALTER TABLE $table ALTER COLUMN $column DROP DEFAULT");
         }