Re-do the fix for stacked graph highlighting
Re-do the fix for stacked graph highlighting

This reverts the change from https://github.com/danvk/dygraphs/pull/211
and instead provides a boolean arg to the plotter so that it can decide
not to draw if needed.

The problem with the approach from #211 is that this prevents error bars
from being highlighted, and those should be redrawn on mouseover.

Fixes issue 424.

grantadesign/dygraphs,mcanthony/dygraphs,kbaggott/dygraphs,danvk/dygraphs,reinert/dygraphs,reinert/dygraphs,grantadesign/dygraphs,Yong-Lee/dygraphs,pshevtsov/dygraphs,petechap/dygraphs,petechap/dygraphs,klausw/dygraphs,panuhorsmalahti/dygraphs,panuhorsmalahti/dygraphs,socib/dygraphs,petechap/dygraphs,panuhorsmalahti/dygraphs,reinert/dygraphs,timeu/dygraphs,reinert/dygraphs,witsa/dygraphs,vhotspur/dygraphs,mcanthony/dygraphs,grantadesign/dygraphs,witsa/dygraphs,klausw/dygraphs,grantadesign/dygraphs,danvk/dygraphs,timeu/dygraphs,mantyr/dygraphs,Yong-Lee/dygraphs,Yong-Lee/dygraphs,vhotspur/dygraphs,mantyr/dygraphs,socib/dygraphs,petechap/dygraphs,panuhorsmalahti/dygraphs,jmptrader/dygraphs,jmptrader/dygraphs,reinert/dygraphs,panuhorsmalahti/dygraphs,mariolll/dygraphs,grantadesign/dygraphs,klausw/dygraphs,davidmsibley/dygraphs,Akiyah/dygraphs,mcanthony/dygraphs,vhotspur/dygraphs,socib/dygraphs,mantyr/dygraphs,mariolll/dygraphs,davidmsibley/dygraphs,mariolll/dygraphs,klausw/dygraphs,Akiyah/dygraphs,klausw/dygraphs,socib/dygraphs,Akiyah/dygraphs,davidmsibley/dygraphs,jmptrader/dygraphs,mcanthony/dygraphs,mantyr/dygraphs,davidmsibley/dygraphs,petechap/dygraphs,danvk/dygraphs,Akiyah/dygraphs,witsa/dygraphs,kbaggott/dygraphs,mcanthony/dygraphs,davidmsibley/dygraphs,vhotspur/dygraphs,mariolll/dygraphs,pshevtsov/dygraphs,mantyr/dygraphs,timeu/dygraphs,timeu/dygraphs,danvk/dygraphs,pshevtsov/dygraphs,kbaggott/dygraphs,kbaggott/dygraphs,Yong-Lee/dygraphs,Yong-Lee/dygraphs,kbaggott/dygraphs,danvk/dygraphs,jmptrader/dygraphs,mariolll/dygraphs,vhotspur/dygraphs,pshevtsov/dygraphs,witsa/dygraphs,Akiyah/dygraphs,jmptrader/dygraphs,witsa/dygraphs,pshevtsov/dygraphs,timeu/dygraphs