Throw an exception when creating a File object for a path that isn't a file

This exception is getting thrown inside of `Project.scan` when it incorrectly parses a path with newlines in it. But the exception gets swallowed by ChildProcess.exec. At least it prevents a file from being created that we don't end up unsubscribing from. But `Project.scan` needs to be improved.

src/app/file.coffee

@@ -9,6 +9,7 @@ class File
   md5: null
 
   constructor: (@path) ->
+    throw "Creating file with path that is not a file: #{@path}" unless fs.isFile(@path)
     @updateMd5()
 
   getPath: ->