Overhaul of type attributes modification

Hi all,

I noticed that if you add, delete, rename or change the type,
collation or precision of a composite type attribute, it deletes all
of them then adds them all back in.  Obviously attribute additions,
deletions and modifications may only occur for types under PostgreSQL
9.1, but I thought it a bit extreme to actually drop all types if
you're adding a new one in, or just removing one.  Also, if you rename
a type, it drops all attributes again then re-adds them, just to have
an attribute with a different name.

So I've attached a patch which "does the right thing".  Take the
example of the following type:

CREATE TYPE bark AS
   (one text,
    two text,
    three text,
    four text,
    five text);

Say we wanted to remove "two", change the type of three to uuid,
rename four to forty and add an extra text type of six.

Normally we'd just get:

ALTER TYPE bark DROP ATTRIBUTE one;
ALTER TYPE bark DROP ATTRIBUTE two;
ALTER TYPE bark DROP ATTRIBUTE three;
ALTER TYPE bark DROP ATTRIBUTE four;
ALTER TYPE bark DROP ATTRIBUTE five;
ALTER TYPE bark ADD ATTRIBUTE one text;
ALTER TYPE bark ADD ATTRIBUTE three text;
ALTER TYPE bark ADD ATTRIBUTE forty uuid;
ALTER TYPE bark ADD ATTRIBUTE five text;
ALTER TYPE bark ADD ATTRIBUTE six uuid;

With these changes we'd now get:

ALTER TYPE bark DROP ATTRIBUTE two;
ALTER TYPE bark RENAME ATTRIBUTE four TO forty;
ALTER TYPE bark ADD ATTRIBUTE six text;

.. except now those are also nicely indented to be more readable for
types with long schemas/type names.

e.g.
ALTER TYPE long_schema_name.quite_a_long_table_name
  ADD ATTRIBUTE "suspiciously long attribute name"?

It also fixes a bug whereby if you have a precision specified, the
word COLLATE mysteriously appears after the type whether or not you
have a collation assigned because the collation condition was based on
the precision being present for some reason.  And if you actually
assigned a collation for a valid data type, it wouldn't appear at all,
so that's fixed too.

--
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
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