This exposed a serious race condition in page_in_from_inode().
Reordered the logic and added a paging lock to VMObject.
Now, only one process can page in from a VMObject at a time.
There are definitely ways to optimize this, for instance by making
the locking be per-page instead. It's not something that I'm going
to worry about right now though.
This only works with the userspace build of SharedGraphics so far.
It's also very slow at loading fonts, but that's easy to fix.
Let's put fonts in /res/fonts/.
