Add support for tickRotor plugin
As of Flot 0.8.3, the tickRotor plugin has to move the tick labels from
opts.ticks to opts.rotatedTicks to avoid a bug. For tooltips, this means
that any content that uses the %y value won't work. Hence, in this
commit we check for use of tickRotor and lookup 'ticks' vs
'rotatedTicks' in the xaxis object as appropriate.
merge pull request and add new contributors