Rickshaw.Graph.RangeSlider.Preview supports millisecond zooming

Changed the domainScale interpolate function to d3.interpolateNumber
(vs. d3.interpolateRound) so that the RangeSlider Preview Window could
zoom into millisecond levels of precision (before it would only allow a
window of 1 second)
Merge pull request #378 from dwt/377_multi_renderer_domain_doesnt_call_sub_renderers_domain

Fix #377: Ensure multi renderer consults it's sub renderers about how th...
Merge pull request #372 from deldrid1/master

Rickshaw.Graph.RangeSlider.Preview supports millisecond zooming
Fix typo
Merge pull request #383 from mo/fix-typo

Fix typo
Ensure Graph creates a copy of the x/yScale before modifying it

x/yScale is coming from the configuration dictionary which may be
referenced by the Graph creator, or shared with other Graphs. We need to
ensure we copy the scale so that our mutations do not change the object
given to us.