change autowrap model to match other terminals
Currently vte moves the cursor beyond the right margin to m_column_count, while other terminal emulators (and VTxxx) keep it at the right margin and just sets a flag. This causes various problems in vte, e.g. it needs to clamp the column when setting tab stops, and when replying to a position query. I just fixed this for tabstops, but there's probably more instances of this around.
So vte should adopt the same model as the other emulators.