Send output files on timeout

The unconventional use of callbacks to return both an error and data
after compilation created a subtle bug where the output files were
dropped by the LockManager in case of an error such as a timeout.

This prevented the frontend to show error logs when a timeout occurs,
creating confusion among users.

We now attach the output files to the error so that they reach the
controller and are sent back to the web service.

test/acceptance/coffee/TimeoutTests.coffee

@@ -15,7 +15,7 @@ describe "Timed out compile", ->
 					\\documentclass{article}
 					\\begin{document}
 					\\def\\x{Hello!\\par\\x}
-					\\x					
+					\\x
 					\\end{document}
 				'''
 			]
@@ -29,3 +29,6 @@ describe "Timed out compile", ->
 	it "should return a timedout status", ->
 		@body.compile.status.should.equal "timedout"
 
+	it "should return the log output file name", ->
+		outputFilePaths = @body.compile.outputFiles.map((x) => x.path)
+		outputFilePaths.should.include('output.log')