Fix slim's complaints about extra render options (:layout)

CHANGELOG.md

@@ -1,6 +1,7 @@
 master
 ===
 
+* Support Slim 2.0 ::Slim::Embedded
 * "middleman build" will clean out old files from the build directory by default now, without needing to pass "--clean". Pass "--no-clean" to disable. #862
 * Allow frontmatter to be side-loaded from a neighboring file with a .frontmatter extension: #855
 * Allow frontmatter "renderer_options" key to overwrite renderer options on a per-file basis. #859
@@ -9,7 +10,6 @@ master
 * :js_assets_paths configuration is deprecated in favor of just calling sprockets.append_path. middleman/sprockets#22
 * Sprockets integration, especially with regard to helper methods, is significantly improved. middleman/sprockets#22
 * Images and fonts from gems added to the Sprockets load path will now be copied to the build output. middleman/sprockets#22 
->>>>>>> Add Sprockets changes to CHANGELOG
 * Added a "t" helper that delegates to I18n.t, just like Rails. #853.
 * I18n will fall back to the default locale if a translation in the current locale is not found. You can disable this behavior by passing `:no_fallbacks => true` when activating `:i18n`. More settings documented at https://github.com/svenfuchs/i18n/wiki/Fallbacks . #853
 * Switched default Markdown engine to Kramdown. #852

middleman-core/lib/middleman-core/core_extensions/rendering.rb

@@ -247,8 +247,9 @@ module Middleman
 
           # Merge per-extension options from config
           extension = File.extname(path)
-          options = opts.merge(options_for_ext(extension))
+          options = opts.dup.merge(options_for_ext(extension))
           options[:outvar] ||= '@_out_buf'
+          options.delete(:layout)
 
           # Overwrite with frontmatter options
           options = options.deep_merge(options[:renderer_options]) if options[:renderer_options]