[web2py] Creating Tables That Allow NULL with MSSQL

[Ross Peoples]

I am running into a problem where web2py creates all the tables in my MSSQL 
database with fields that do not allow NULL values. This is regardless of 
the notnull=False setting on the fields.

I am using mssql:// as the adapter and having web2py create table 
structures. A test table definition:

db.define_table('test_table',
    Field('field_allows_null', notnull=False),
    Field('field_rejects_null', notnull=True)
)

In MSSQL, both fields will get created to reject NULL values.