Issue #301:  use forward slash for temp_files

This is what I've been running for quite a while to avoid issue #301: Git! commands broken in windows.  

It's absurdly hackish and there's probably a better solution, but it's been running without problems for quite a while on all my *nix and windows boxes.    Apparently, &lt;amatch&gt;:p always uses forward slashes on windows, I haven't looked at the vim source to figure out why or if there's an exception to that, but using forward slashes for all the entries in temp_files is a quick fix to the problem.