Fixes window dragging in uncomposited metacity.

It's not an offset from pixmap coords to composited pixmap coords,
it's an offset from screen-relative window drawable coords to
composited pixmap coords.

There's a limitation still for RepeatNone, but this fixes a bunch of
fallbacks for gnome-terminal.

Fixes failure in rendercheck -t blend -o src

Fixes failure with rendercheck.

This doesn't yet have an optimized glamor_composite_rects()
implementation, but it does triple the speed of x11perf -aa10text.

fb/pixman demand this alignment, and all sorts of things go badly otherwise.
Fixes piglit x11-8bpp-7x8-draw.

Window dragging with metacity+gnome-terminal+xcompmgr is almost credible.

Here's my theory for the flipping: It doesn't really matter which
orientation we store the pixmaps if we don't scan them out.  We have
to flip coordinates for the window system framebuffer.  Doing so for
everything else makes things consistent.  I'm not sure how this will
interact with future GLX integration, though.

Apparently I don't have anything hitting this path, so I'm not sure if
it's good or not.

Mostly fixes gnome-terminal text.

Root weave displays. \o/

Bringup is really not flying when I can't see anything.  So dump back
to all software so I can turn on a bit at a time.

This should avoid a bunch of absurdity with GLX front buffer handling,
fix exposes, and improve performance.  For now we're copying the whole
buffer while glamor is developed.