add table header tests
add table header tests

for #1015

becompany/dc.js,dc-js/dc.js,ruhley/dc.js,ruhley/dc.js,r4j4h/dc.js,aaronhoffman/dc.js,mtraynham/dc.js,r4j4h/dc.js,Hauenstein/dc.js,maackle/dc.js,TheDataShed/dc.js,becompany/dc.js,aaronhoffman/dc.js,maackle/dc.js,ruhley/dc.js,maackle/dc.js,mtraynham/dc.js,dc-js/dc.js,becompany/dc.js,aaronhoffman/dc.js,aaronhoffman/dc.js,mtraynham/dc.js,r4j4h/dc.js,Hauenstein/dc.js,mtraynham/dc.js,TheDataShed/dc.js,ruhley/dc.js,Hauenstein/dc.js,maackle/dc.js,aaronhoffman/dc.js,TheDataShed/dc.js,mtraynham/dc.js,Hauenstein/dc.js,r4j4h/dc.js,dc-js/dc.js,maackle/dc.js,Hauenstein/dc.js,TheDataShed/dc.js,r4j4h/dc.js,ruhley/dc.js,dc-js/dc.js,dc-js/dc.js,TheDataShed/dc.js