Don't delete knitr cache files

app/coffee/ResourceWriter.coffee

@@ -46,7 +46,7 @@ module.exports = ResourceWriter =
 				do (file) ->
 					path = file.path
 					should_delete = true
-					if path.match(/^output\./) or path.match(/\.aux$/)
+					if path.match(/^output\./) or path.match(/\.aux$/) or path.match(/^cache\//) # knitr cache
 						should_delete = false
 					if path == "output.pdf" or path == "output.dvi" or path == "output.log"
 						should_delete = true

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)
@@ -81,6 +83,11 @@ describe "ResourceWriter", ->
 				.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