Merge branch multiple-texture-rectangle into master

Merge branch multiple-texture-rectangle into master

Bug 1289 - Draw multiple glyphs at once

The multiple-texture-rectangle branch adds a new Cogl texture function
called cogl_texture_multiple_rectangles which is used to draw multiple
rectangles out of a texture using a single GL call. This is
significantly faster than drawing the rectangles with individual calls
on some platforms. The Pango renderer now uses this to speed up
rendering.

The conflicts are just due to the whitespace fixes in cb569a5.

Conflicts:

	clutter/cogl/gl/cogl-context.c
	clutter/cogl/gl/cogl-context.h
	clutter/cogl/gl/cogl-texture.c