Add local file support.

Example of absolute path to local file.
```html:/home```

Example of relative path to local file.
```html:home```

1.8.7 string fix. 's'[0..0] instead of 's'[0]

Fix regex.

Add absolute and relative tests.

lib/gollum/frontend/app.rb

@@ -89,12 +89,6 @@ module Precious
       redirect File.join(settings.wiki_options[:base_path].to_s, 'Home')
     end
 
-    # Removes all slashes from the start of string.
-    def clean_url url
-      return url if url.nil?
-      url.gsub('%2F','/').gsub(/^\/+/,'')
-    end
-
     # path is set to name if path is nil.
     #   if path is 'a/b' and a and b are dirs, then
     #   path must have a trailing slash 'a/b/' or

lib/gollum/frontend/helpers.rb

@@ -17,5 +17,11 @@ module Precious
     def sanitize_empty_params(param)
       [nil,''].include?(param) ? nil : CGI.unescape(param)
     end
+
+    # Remove all slashes from the start of string.
+    def clean_url url
+      return url if url.nil?
+      url.gsub('%2F','/').gsub(/^\/+/,'')
+    end
   end
 end