auto merge of #466 : pcwalton/servo/phantom-type, r=pcwalton

See the explanation on the commit for more detail.

r? @metajack
Initial support for line-height. Does not take vertical-align into account but does align baselines based on the largest box.
Update the gitignore list for the new component directory.
auto merge of #493 : jrfeenst/servo/line-height, r=pcwalton

This calculates the line-height of each line box based on the tallest box in the line. It then lines up the baselines of all the other boxes.