NH-2861

Here's a patch for NH-2861, allowing filters to work in combination with <join> mappings. 

Here's the Jira link: https://nhibernate.jira.com/browse/NH-2861

Here's a mailing list item on the issue: http://groups.google.com/group/nhusers/browse_thread/thread/1259723b6d11a16e/d064b3d8b4406a46?lnk=gst&q=join+filter#d064b3d8b4406a46

The fix also allows filters to use property names instead of column names. I added this because it's possible (and even common) to have repeated column names in a class mapped with `<join>`. The precedence behavior is as follows:

1. if the filter references a property, use it
2. if a filter references a column on the "primary" table use it
3. if the filter references a column on a "secondary" table use it. The relative precedence of columns in the secondary table is undefined.

I hope that makes sense. I'd appreciate any feedback on the patch.