Issue #344: bql: column name specified via AS can't be used in WHERE (blais/beancount)

[Martin Michlmayr]

New issue 344: bql: column name specified via AS can't be used in WHERE
https://bitbucket.org/blais/beancount/issues/344/bql-column-name-specified-via-as-cant-be

Martin Michlmayr:

I specify a column name via "AS foo" but then "WHERE foo" says that "foo" is an invalid column. It would be nice if it would recognise the custom column names I make via "AS".

```
beancount> SELECT ANY_META('entity') as entity WHERE ANY_META('entity') ~ 'Michlmayr';
entity
---------
Michlmayr
Michlmayr
Michlmayr
Michlmayr
beancount> SELECT ANY_META('entity') as entity WHERE entity ~ 'Michlmayr';
ERROR: Invalid column name 'entity' in WHERE clause context.
beancount>
```