Fix warnings in mesh tests

	Fix warnings in mesh tests

	* tests/conform/test-mesh-mutability.c (on_paint):
	* tests/conform/test-mesh-interleved.c (on_paint):
	* tests/conform/test-mesh-contiguous.c (on_paint): Use g_usleep
	instead of sleep

	* tests/conform/test-mesh-mutability.c (queue_redraw):
	* tests/conform/test-mesh-interleved.c (queue_redraw):
	* tests/conform/test-mesh-contiguous.c (queue_redraw): Added
	missing return statement

	* clutter/cogl/cogl-mesh.h: Add a declaration for
	cogl_mesh_submit

	* clutter/cogl/common/cogl-mesh.c (cogl_mesh_submit): Move the
	documentation to cogl-mesh.h to match the rest of the functions