Print baserestrictinfo for varchar fields

Hi,

I noticed that debug_print_rel outputs "unknown expr" when the fields
in baserestrictinfo are typed as varchar.

create table tbl_a(id int, info varchar(32));

RELOPTINFO (tbl_a): rows=4 width=86
        baserestrictinfo: unknown expr = pattern

My approach is to handle the RelabelType case in print_expr. After
the patch, I get:

RELOPTINFO (tbl_a): rows=4 width=86
        baserestrictinfo: tbl_a.info = pattern

I wonder if this is a proper way of fixing it?

Thank you,
Donald Dong