fix issue of pie chart being invisible when total group value is 0
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.
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
Fixes row test case that was comparing key values of the SVG to the filters.  The key is numeric and not a string.
allowing composite charts to toggle the legend
FIX #579 Maintain brushOn when redrawing series chart with new data
adding tests
adding test
Expose geo-choropleth's path object
Added text option for number-display
Number-display - Hide entries if the value is 0
Added Pluralization
Added .html({singular:'',plural:'',zero:''} for number-display
Added .html function. Issue #527 and #619
Corrected number.html accordingly
Replaced == with === and added getter functions
Merge remote-tracking branch 'upstream/master'
Added test-specs
update d3.js and fix a nonsensical test it broke