Escape filenames in regexes. Fixes #942.

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

@@ -196,7 +196,7 @@ module Middleman::CoreExtensions
     end
 
     def normalize_path(path)
-      path.sub(%r{^#{app.source_dir}\/}, "")
+      path.sub(%r{^#{Regexp.escape(app.source_dir)}\/}, "")
     end
   end
 end

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

@@ -191,7 +191,7 @@ module Middleman
             engine = File.extname(resource.source_file)[1..-1].to_sym
 
             # Look for partials relative to the current path
-            relative_dir = File.join(current_dir.sub(%r{^#{self.source_dir}/?}, ""), data)
+            relative_dir = File.join(current_dir.sub(%r{^#{Regexp.escape(self.source_dir)}/?}, ""), data)
 
             # Try to use the current engine first
             found_partial, found_engine = resolve_template(relative_dir, :preferred_engine => engine, :try_without_underscore => true)

middleman-core/lib/middleman-more/core_extensions/default_helpers.rb

@@ -124,7 +124,7 @@ class Middleman::CoreExtensions::DefaultHelpers < ::Middleman::Extension
       # If the basename of the request as no extension, assume we are serving a
       # directory and join index_file to the path.
       path = File.join(asset_dir, current_path)
-      path = path.sub(/#{File.extname(path)}$/, ".#{asset_ext}")
+      path = path.sub(/#{Regexp.escape(File.extname(path))}$/, ".#{asset_ext}")
 
       yield path if sitemap.find_resource_by_path(path)
     end