Fix getColumnNearX for nested insets

Fix getColumnNearX for nested insets

The horizontal position of the inset was not taken in account.
The rounding is not always the same as with the old code, but this
is not really important.

Additional changes:

 * improve debug output of rows

 * remove Bidi& argument of the RowPainter constructor, since it is always
   an empty Bifi that is passed. This means that the Bidi class is not
   used at all any more in TextMetrics.cpp. The only remaining user is
   RowPainter.