More DROP COLUMN

OK,

DROP COLUMN now seems to work perfectly.  All the old test cases that failed
now work fine.

However, I'm not happy with the way dropped columns are renamed.  I want to
give them a name that no-one would ever want to use as a legit column name.
I don't like this behaviour:

test=# create table test (a int4, b int4);
CREATE TABLE
test=# alter table test drop a;
ALTER TABLE
test=# select dropped_1 from test;
ERROR:  Attribute "dropped_1" not found
test=# alter table test add dropped_1 int4;
ERROR:  ALTER TABLE: column name "dropped_1" already exists in table "test"

It's a bit confusing, hey?

What should we do about it?

Maybe I could make ADD COLUMN give this message instead for dropped columns?

ERROR:  ALTER TABLE: column name "dropped_1" is a dropped column in table
"test" ... or something ...

We could name the fields "________dropped_x" sort of thing perhaps????

Chris