transpile doesn't allow backslashes in filename

[ivogabe]

ts.transpile('var x;', {}, 'a\\b.ts');

This gives an error:

                throw new Error("Debug Failure. False expression: " + (message
                      ^
Error: Debug Failure. False expression: Output generation failed
    at Object.assert ([..]/node_modules/typescript/lib/typescript.js:1573:23)
    at transpileModule ([..]/node_modules/typescript/lib/typescript.js:42895:18)
    at Object.transpile ([..]/node_modules/typescript/lib/typescript.js:42903:22)
    at Object.<anonymous> ([..]/api-test.js:16:4)
    at Module._compile (module.js:460:26)
    at Object.Module._extensions..js (module.js:478:10)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Function.Module.runMain (module.js:501:10)
    at startup (node.js:129:16)

Using forward slashes does work.
Discovered by @arogg at ivogabe/gulp-typescript#199. I've fixed it in gulp-typescript by replacing all backward slashes with forward ones, but I think it should be fixed here too.