Call to `getXDomain` requires targets.

Error can be reproduced here:
http://jsfiddle.net/mikwat/bt8u9fh9/1/
resize the eventRect for single data points for tooltips to work
api: allow querying chart range
Merge branch 'master' into tooltip-fix-single-data-point

Conflicts:
	c3.min.js
Fix bar width on subchart when brush - #497
Fix conflict
Merge branch 'chriskalmar-tooltip-fix-single-data-point'
Fix for v0.3
Merge branch 'mikwat-master'
Fix axis.x.default
Fix tick text rotation with negative value - #501
Add oninit option - #502
Fix the boundary of x domain when zooming - #505
Fix x and index of tooltip.show API - #509
Add axis.x.extent option instead of axis.x.default - #512
Fix legend position to be centered - #515
Refactor data.onclick
Fix grid and region when arc tyle - #518
Fix update x domain for flow
Fix update x domain for flow