Preparsing of ALTER statements by sqlcmd

These changes allow sqlcmd to execute ad hoc `ALTER TABLE ... ALTER` and `ALTER TABLE ... DROP` statements.

I found that Web Studio currently will not insert semicolons before `ALTER` statements, so I didn't need to do anything there.  Instead I just added GEB tests that characterize this behavior.  Note: to make the GEB tests work, I added `schema="ddl"` to the genqa default deployment file.