fix issue of pie chart being invisible when total group value is 0
Added support for RequireJS AMD.
Fixes bug 497.  Changed baseMixin filterHandler to correctly handle filtering dates.  We use a trick from Crossfilter 'a <= b && a >= b' instead of 'a == b' because the former coerces the values to primitives which then works for dates.
Moves references to dc.renderAll or dc.redrawAll to _chart.redrawGroup & _chart.renderGroup respectively.  More conventional with other charts and allows easier overriding.
Minor fixes to removeFilter and hasFilter that are congruent with the changes in filterHandler.  filters may be dates, thus indexOf will not work.
Merge branch 'master' into fix_bug_497
Merge master
Fixes row test case that was comparing key values of the SVG to the filters.  The key is numeric and not a string.
Fixes bug 551
Merge pull request #562
merge #562

Thanks @mtraynham!
cut duplicate of function

fixed #571
allowing composite charts to toggle the legend
FIX #579 Maintain brushOn when redrawing series chart with new data
update d3
inconsequential changes due to library updates
Merge branch 'master' into merge526

Conflicts:
	dc.min.js
	dc.min.js.map
add amd support

based on PR #526 (thanks @spacelis!)
but without any pollution, as implemented in d3 here:
https://github.com/mbostock/d3/commit/99ff885b960309f03ca5142ada3fcfe1a56f8604
adding tests
adding test