Add docs about the 'new' restriction on excludes.

site/docs/configuration.md

@@ -67,7 +67,7 @@ class="flag">flags</code> (specified on the command-line) that control them.
         <p class="description">
           Exclude directories and/or files from the
           conversion. These exclusions are relative to the site's
-          source directory.
+          source directory and cannot be outside the source directory.
         </p>
       </td>
       <td class='align-center'>

test/test_entry_filter.rb

@@ -72,7 +72,7 @@ class TestEntryFilter < Test::Unit::TestCase
     end
   end
 
-  context "glob_include?" do
+  context "#glob_include?" do
     setup do
       stub(Jekyll).configuration do
         Jekyll::Configuration::DEFAULTS.merge({'source' => source_dir, 'destination' => dest_dir})