Implement paginated create_similar, moving similar images down to PS and PDF.

The new paginated create_similar simply forwards to target backend create_similar.

We maintain the fact that PS and PDF surfaces are returning image
surfaces for create_similar by moving that explicitly to their own
create_similar functions.

(This commit is the combination of the following original commits:

	6b69e8c012adb4f2fc2ee9c1579fed8214e8f510
	2589db92a4395f8e900dbc4eafc45982f0d985d3
)

src/cairo-paginated-surface.c

@@ -79,12 +79,6 @@ const cairo_private cairo_surface_backend_t cairo_paginated_surface_backend;
 static cairo_int_status_t
 _cairo_paginated_surface_show_page (void *abstract_surface);
 
-/* XXX: This would seem the natural thing to do here. But currently,
- * PDF and PS surfaces do not yet work as source surfaces. So instead,
- * we don't implement create_similar for the paginate_surface which
- * means that any create_similar() call on a paginated_surfacae will
- * result in a new image surface. */
-#if 0
 static cairo_surface_t *
 _cairo_paginated_surface_create_similar (void			*abstract_surface,
 					 cairo_content_t	 content,
@@ -95,7 +89,6 @@ _cairo_paginated_surface_create_similar (void			*abstract_surface,
     return cairo_surface_create_similar (surface->target, content,
 					 width, height);
 }
-#endif
 
 cairo_surface_t *
 _cairo_paginated_surface_create (cairo_surface_t				*target,
@@ -471,7 +464,7 @@ _cairo_paginated_surface_snapshot (void *abstract_other)
 
 const cairo_surface_backend_t cairo_paginated_surface_backend = {
     CAIRO_INTERNAL_SURFACE_TYPE_PAGINATED,
-    NULL, /* create_similar --- see note for _cairo_paginated_surface_create_similar */
+    _cairo_paginated_surface_create_similar,
     _cairo_paginated_surface_finish,
     _cairo_paginated_surface_acquire_source_image,
     _cairo_paginated_surface_release_source_image,

src/cairo-pdf-surface.c

@@ -456,10 +456,11 @@ _cairo_pdf_surface_create_similar (void		       *abstract_src,
 				   int			width,
 				   int			height)
 {
-    cairo_pdf_surface_t *template = abstract_src;
+    cairo_format_t format = _cairo_format_from_content (content);
 
-    return _cairo_pdf_surface_create_for_document (template->document,
-						   width, height);
+    /* Just return an image for now, until PDF surface can be used
+     * as source. */
+    return cairo_image_surface_create (format, width, height);
 }
 
 static cairo_pdf_stream_t *

src/cairo-ps-surface.c

@@ -780,6 +780,19 @@ _word_wrap_stream_create (cairo_output_stream_t *output, int max_column)
 					NULL, stream);
 }
 
+static cairo_surface_t *
+_cairo_ps_surface_create_similar (void		       *abstract_src,
+				   cairo_content_t	content,
+				   int			width,
+				   int			height)
+{
+    cairo_format_t format = _cairo_format_from_content (content);
+
+    /* Just return an image for now, until PS surface can be used
+     * as source. */
+    return cairo_image_surface_create (format, width, height);
+}
+
 static cairo_status_t
 _cairo_ps_surface_finish (void *abstract_surface)
 {
@@ -1634,7 +1647,7 @@ _cairo_ps_surface_set_paginated_mode (void			*abstract_surface,
 
 static const cairo_surface_backend_t cairo_ps_surface_backend = {
     CAIRO_SURFACE_TYPE_PS,
-    NULL, /* create_similar */
+    _cairo_ps_surface_create_similar,
     _cairo_ps_surface_finish,
     NULL, /* acquire_source_image */
     NULL, /* release_source_image */