ADD PRIMARY KEY and ADD UNIQUE

Hi,

Tom - you mentioned recently that your changes to the parser mean that my
add unique code is deprecated. You also mentioned that your changes will
make ADD PRIMARY KEY also work.

If that is true, then the fact that both of these work should be put in the
HISTORY file (ADD UNIQUE already is) and documented on the ALTER TABLE docs.
This should probably be done before a release.

Also, I don't know if this should be done so late in the cycle, but the ADD
UNIQUE regression test I added should probably be copied as an ADD PRIMARY
KEY regression test...

Chris