Fix nested comment handling

[mchakravarty]

• Nested comment tokens are sometimes not properly syntax highlighted.
  • How do we trigger the layout manager to validate rendering attributes again (for a larger range). We might have to invalidate the layout.
  • There also seems to be a problem with the updating of line map information.
• After invalidation due to a multiple comment start token, the minimap doesn't redraw from the line of the change onward. This is now covered by Unreliable minimap redraw #99.