Reserved keywords in the sql causing problems

[zeebo]

The schema to create the table for the following model fails on sqlite3:

model entry (
	key   pk
	field pk   serial64
	field when utimestamp
)

The problem is when is a keyword and confuses things. There's a workaround: just add a column directive like

model entry (
	key   pk
	field pk   serial64
	field when utimestamp (column _when)
)

but it'd be nice if DBX did this for you.