Match by filename does not work on Windows

[Grueslayer]

Because the filename strip is done with the slash "/" as separator, it does not work under windows using backslash "\".

Possible solution for pymatcher.py

  def filename_score(line):
        # get filename via reverse find to improve performance
        shellslash = vim.eval('!exists("+shellslash")?"/":&shellslash?"/":"\\\\"')      
        slashPos = line.rfind(shellslash)