Improve handling of files which have just ALTER statements in them

[worksofliam]

Since we recommend alter files should be in a separate file, we need a way to have a target which doesn't result in an object (for files with ALTER) statements

[edmundreinhardt]

I thought that the ALTER statements would be included in the same file as CREATE OR REPLACE TABLE. does that not work?

[worksofliam]

@edmundreinhardt Right now, no. ALTER statements can create circular deps very easily.

For example, two files:

1. CREATE TABLE DEPARTMENT, with an ALTER which adds a reference to table EMPLOYEE
2. CREATE TABLE EMPLOYEE with an ALTER which adds a reference to table DEPARTMENT

This circular dep is bad. Moving those alters to separate files will allow us to resolve this issue.