Get ignores varchar(max) conditions for MSSQL

[btrepp]

From go-gitea/gitea#697

It appears that
has, err := x.Get(&PublicKey{ Content: content, Type: KeyTypeUser, })
Where content is of type varchar(max). The content query condition is ignored. This ends up checking on the type condition, and returning incorrect values.

MSSQL does support querying on text columns. Eg the below works
has, err := x.Where("content=?",content).Where("type=?",KeyTypeUser).Get(&PublicKey{})

Go-xorm should either support that in the "bean" or error out if it is not supported. Silently dropping it leads to unexpected results.

[lunny]

This is because MSSQL don't support use TEXT column as query condition. So xorm will ignore it.