* Cleaned out export related visibility in Session, and simpified Session <--> export component communication in general
* Removed export_status.h header dependency from session.h
* Added check for libsndfile FLAC and Ogg Vorbis compatibility
* Added ExportFileFactory, leading in cleaner code in ExportProcessor, and better extensibility for possible future non-libsndfile formats
git-svn-id: svn://localhost/ardour2/branches/3.0@3818 d708f5d6-7413-0410-9779-e7cbd77b26cf