bake: Improve render context and bake record, fix incremental bake bugs. * Used sources and taxonomies are now stored on a per-render-pass basis. This fixes bugs where sources/taxonomies were used for one pass, but that pass is skipped on a later bake because its result is cached. * Bake records are now created for all pages even when they're not baked. Record collapsing is gone except for taxonomy index pages. * Bake records now also have sub-entries in order to store information about each sub-page, since some sub-pages could use sources/taxonomies differently than others, or be missing from the output. This lets PieCrust handle clean/dirty states on a sub-page level.

--- a/piecrust/routing.py	Sat Apr 04 07:55:49 2015 -0700
+++ b/piecrust/routing.py	Mon Apr 06 19:59:54 2015 -0700
@@ -239,7 +239,8 @@
                 else:
                     registered_values = tuple(values)
                 eis = self.app.env.exec_info_stack
-                eis.current_page_info.render_ctx.used_taxonomy_terms.add(
+                cpi = eis.current_page_info.render_ctx.current_pass_info
+                cpi.used_taxonomy_terms.add(
                         (self.source_name, self.taxonomy_name,
                             registered_values))