ALTER TABLE documentation

I just noticed that the current ALTER TABLE documentation doesn't do a
very good job differentiating between commands that affect the whole
table and commands that only affect specific columns.

http://developer.postgresql.org/pgdocs/postgres/sql-altertable.html

That didn't matter as much before, but now that we have both
table-level options and attribute-level options, there are two
sections in there that look all-too-similar...  suggestions?

...Robert