Don't delete knitr cache files

test/unit/coffee/ResourceWriterTests.coffee

@@ -55,6 +55,8 @@ describe "ResourceWriter", ->
 			}, {
 				path: "extra.aux"
 				type: "aux"
+			}, {
+				path: "cache/_chunk1"
 			}]
 			@resources = "mock-resources"
 			@OutputFileFinder.findOutputFiles = sinon.stub().callsArgWith(2, null, @output_files)
@@ -80,6 +82,11 @@ describe "ResourceWriter", ->
 			@ResourceWriter._deleteFileIfNotDirectory
 				.calledWith(path.join(@basePath, "extra.aux"))
 				.should.equal false
+		
+		it "should not delete the knitr cache file", ->
+			@ResourceWriter._deleteFileIfNotDirectory
+				.calledWith(path.join(@basePath, "cache/_chunk1"))
+				.should.equal false
 
 		it "should call the callback", ->
 			@callback.called.should.equal true