protocol: add sub-surfaces

Add protocol for sub-surfaces, wl_subcompositor as the global interface,
and wl_subsurface as the per-surface interface extension.

This patch is meant to be reverted, once sub-surfaces are moved into
Wayland core.

Changes in v2:

- Rewrite wl_subcompositor.get_subsurface description, and move mapping
  and commit details into wl_subsurface description. Check the wording
  in wl_subsurface.set_position description.

- Add wl_subsurface.set_commit_mode request, and document it, with the
  commit_mode enum. Add bad_value error code for wl_subsurface.

- Moved the protocol into Weston repository so we can land it upstream
  sooner for public exposure. It is to be moved into Wayland core later.

- Add destroy requests to both wl_subcompositor and wl_subsurface, and
  document them. Experience has showed, that interfaces should always
  have a destructor unless there is a good and future-proof reason to not
  have it.

Changes in v3:

- Specify, that wl_subsurface will become inert, if the corresponding
  wl_surface is destroyed, instead of requiring a certain destruction
  order.

- Replaced wl_subsurface.set_commit_mode with wl_subsurface.set_sync and
  wl_subsurface.set_desync. Parent-cached commit mode is now called
  synchronized, and independent mode is desynchronized. Removed
  commit_mode enum, and bad_value error.

- Added support for nested sub-surfaces.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

src/.gitignore

@@ -18,3 +18,6 @@ workspaces-protocol.c
 workspaces-server-protocol.h
 input-method-protocol.c
 input-method-server-protocol.h
+subsurface-server-protocol.h
+subsurface-protocol.c
+

src/Makefile.am

@@ -36,6 +36,8 @@ weston_SOURCES =				\
 	input-method-server-protocol.h		\
 	workspaces-protocol.c			\
 	workspaces-server-protocol.h		\
+	subsurface-protocol.c			\
+	subsurface-server-protocol.h		\
 	bindings.c				\
 	animation.c				\
 	gl-renderer.h				\
@@ -280,6 +282,8 @@ BUILT_SOURCES =					\
 	input-method-server-protocol.h		\
 	workspaces-server-protocol.h		\
 	workspaces-protocol.c			\
+	subsurface-server-protocol.h		\
+	subsurface-protocol.c			\
 	git-version.h
 
 CLEANFILES = $(BUILT_SOURCES)

src/compositor.h

@@ -35,6 +35,7 @@ extern "C" {
 #include "version.h"
 #include "matrix.h"
 #include "config-parser.h"
+#include "subsurface-server-protocol.h"
 
 #define ARRAY_LENGTH(a) (sizeof (a) / sizeof (a)[0])