I am working on providing users a wizard for creating queries.  I have it working, but occassionally get the message "Entity 'Task' is not supported for semi join inner selects"

The query resembles this...

select id, name from opportunity where id in (select whatid from Task where type = 'special activity type')

I totally understand that some objects cannot be used in this type of filter.  In the UI where they create the rule that generates this query, I want to EXCLUDE objects that do not support this kind of filtering (e.g. Tasks, Activity History, etc).  Looking at the describe information, I cannot figure out a way to determine this.  

Is there anything in the object or field describe that tells me this?