Properly handle resizing the captured output table. It didn't like having its frame set because the height depends on the width.
Fix memory leak and over-releasing of PTYSession in announcements
Add some intercell spacing to captured output to improve legibility.
Cache the last command mark. Search the last 500 marks for a last command mark (not just the last 50) if it's not cached. Add a delegate to iTermMark to notify VT100Screen when a mark becomes a command mark.