Make display:auto respect cascading styles

This is a proposal to change the meaning of `display: auto` so that it leaves the final value up to the stylesheets, stripping the inline `display` property off entirely. 

Much of the time, this gives the same effect as the previous `getDisplayType` logic, since elements will simply revert to their natural default display type. But now the user has fine-grained control over which `display` value is ultimately used.

Alternatively, if people really like the current meaning of `display: auto`, I could also see this new semantic being given a different name, like `display: blank` or `display: cascade`.