Improve error stacks for Filer/MakeDrive

[humphd]

In certain cases, when there's an error thrown deep in code that uses filer/makedrive, we get something like this:

  1) MakeDrive Client SyncFileSystem and Conflicts should allow fs.rename:
     Uncaught Error
    at module.exp
  rts (/Users/dave/Sites/repos/makedrive/client/thirdparty/filer/src/errors.js:83:32)
      at Array.forEach (native)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/client/thirdparty/filer/src/errors.js:74:3)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/client/thirdparty/filer/src/providers/indexeddb.js:5:14)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/client/thirdparty/filer/src/providers/index.js:1:79)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/client/thirdparty/filer/src/filesystem/interface.js:14:17)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/client/thirdparty/filer/src/index.js:2:15)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/lib/filer.js:1:80)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/server/lib/filesystem.js:1:75)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/tests/lib/util.js:4:18)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at Object.<anonymous> (/Users/dave/Sites/repos/makedrive/tests/unit/client/sync-filesystem.js:2:12)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
      at /usr/local/lib/node_modules/mocha/lib/mocha.js:152:27
      at Array.forEach (native)
      at Mocha.loadFiles (/usr/local/lib/node_modules/mocha/lib/mocha.js:149:14)
      at Mocha.run (/usr/local/lib/node_modules/mocha/lib/mocha.js:306:31)
      at Object.<anonymous> (/usr/local/lib/node_modules/mocha/bin/_mocha:339:7)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Function.Module.runMain (module.js:497:10)
      at startup (node.js:119:16)
      at node.js:906:3

This appears to mean that Filer's Error code is trying to create a Filer error, and it can't for some reason so crashes. We should be creating an Unknown error and giving a proper err/stack.

[humphd]

Fixed in Filer, and I'll pull it in with issue #3