noverlay branch

[Stefan Monnier]

I just updated the noverlay branch to the code in `master` (most of it
was mechanical except for the fact that since the last commit on that
branch we have gotten rid of Lisp_Misc and we moved to pdumper).

I'm getting ready to install this in `master`, so I'd encourage people
to try this code as much as possible to try and weed out the most
glaring problems before it hits master.  The code generally looks good,
but it touches some quite "core" code in the redisplay (with lots of
off-by-one opportunities) and in the memory management (with
opportunities for crashes and memory leaks).

For those who're not familiar with this branch, it changes the way
overlays are stored in a buffer: instead of keeping them in naïve
singly-linked lists, it keeps them in balanced binary trees, so as to
replace an O(N) complexity with O(log N). This way Emacs should not get
sluggish even with millions of overlays (of course, if a given buffer
position is covered by a million overlays, it'll still be sluggish when
operating around that position).


        Stefan