Fixes #8483 Windows completion error

This should fix #8483 I am not a Julia power user yet so could some of you guy's check it's working because I have not compiled base with it, @lucasb-eyer, @tkelman?
I have no objection in removing it. Lucas could you try and give 257 and 259 a look and see if you can think/find any undesireable behivor on Linux caused by these lines? These two lines is also needed to get spaces in paths working on windows and Linux.