ADD CONSTRAINT UNIQUE patch

Hi all,

Here is my much-promised patch to let people add UNIQUE constraints after
table creation time.  Big deal you say - but this patch is the basis of the
next thing which is adding PRIMARY KEYs after table creation time.  (Which
is currently impossible without twiddling catalogs)

Rundown
-------

* I have made the makeObjectName function of analyze.c non-static, and
exported it in analyze.h

* I have included analyze.h and defrem.h into command.c, to support
makingObjectNames and creating indices

* I removed the 'case CONSTR_PRIMARY' clause so that it properly fails and
says you can't add primary keys, rather than just doing nothing and
reporting nothing!!!

* I have modified the docs.

Algorithm
---------

* If name specified is null, search for a new valid constraint name.  I'm
not sure if I should "lock" my generated name somehow tho - should I open
the relation before doing this step?

* Open relation in access exclusive mode

* Check that the constraint does not already exist

* Define the new index

* Warn if they're doubling up on an existing index

Chris