KMS Font Rendering

Font rendering now works with the KMS Glamo driver.  The problem was that a particular case of the trickiest EXA function ("ModifyPixmapHeader") wasn't handled correctly.  The easy fix was to remove our implementation of that hook altogether and let EXA handle it on its own.  To make this work properly, a new function (with similar but more limited functionality) had to be added to deal with the initialisation of the front buffer, like this.

So now, apart from whatever gremlins might be lurking deep in the code, the KMS driver should be on an even footing with the non-KMS version.  Before getting on with Mesa and other such fun stuff, I'd still like to get to the bottom of the GEM hashtable corruption that seems to happen after a long time (more than a day) of operation.  Additionally, there's a small issue with the width of the screen that happens with recent versions of X.org (1.6.1 and later at the very least), but that isn't specific to KMS.

For an up-to-date list of "things that are bothering me" like these, see this new page.  Call it an unofficial project status page.