ChangeHandler: Don't hexify text columns.

As far as I understand, it doesn't make any sense to hexify text
columns; they break in many ways (you can't roundtrip the UTFs,
quote_val gets the hex quoting wrong, etc) and in any case,
the maatkit bugs about the feature are all about blob/binary
columns.

And, while a perilous excercise of genetic programming, removing
it didn't break any pt-table-sync tests, so this commit does
exactly that.

lib/ChangeHandler.pm

@@ -496,7 +496,7 @@ sub make_fetch_back_query {
          map {
             my $col = $_;
             if (    $self->{hex_blob}
-                 && $tbl_struct->{type_for}->{$col} =~ m/blob|text|binary/ ) {
+                 && $tbl_struct->{type_for}->{$col} =~ m/b(?:lob|inary)/ ) {
                # Here we cast to binary, as otherwise, since text columns are
                # space padded, MySQL would compare ' ' and '' to be the same.
                # See https://bugs.launchpad.net/percona-toolkit/+bug/930693