File.absolute_path isn't available on 1.8.

For vcr#118.

lib/vcr/configuration.rb

@@ -114,8 +114,8 @@ def initialize
     #   end
     attr_reader :cassette_library_dir
     def cassette_library_dir=(cassette_library_dir)
-      @cassette_library_dir = cassette_library_dir ? File.absolute_path(cassette_library_dir) : nil
-      FileUtils.mkdir_p(@cassette_library_dir) if cassette_library_dir
+      FileUtils.mkdir_p(cassette_library_dir) if cassette_library_dir
+      @cassette_library_dir = cassette_library_dir ? absolute_path_for(cassette_library_dir) : nil
     end
 
     # Default options to apply to every cassette.
@@ -350,6 +350,10 @@ def start_new_fiber_for(request, block)
         fiber.resume(request.fiber_aware)
       end
     end
+
+    def absolute_path_for(path)
+      Dir.chdir(path) { Dir.pwd }
+    end
   end
 end
 

spec/vcr/configuration_spec.rb

@@ -14,8 +14,10 @@
     end
 
     it 'resolves the given directory to an absolute path, so VCR continues to work even if the current directory changes' do
-      subject.cassette_library_dir = 'tmp/cassette_library_dir/new_dir'
-      subject.cassette_library_dir.should eq(File.absolute_path(tmp_dir))
+      relative_dir = 'tmp/cassette_library_dir/new_dir'
+      subject.cassette_library_dir = relative_dir
+      absolute_dir = File.join(VCR::SPEC_ROOT.sub(/\/spec\z/, ''), relative_dir)
+      subject.cassette_library_dir.should eq(absolute_dir)
     end
   end