Fix directory completion for different file-systems
Fix directory completion for different file-systems

Use the file-system agnostic `System.IO.Path.DirectorySeparatorChar` for
`GetReplacementTextForDirectory`, instead of hard-coded backslashes.

JamesWTruher/PowerShell-1,kmosher/PowerShell,daxian-dbw/PowerShell,daxian-dbw/PowerShell,bingbing8/PowerShell,PaulHigin/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,KarolKaczmarek/PowerShell,bmanikm/PowerShell,bingbing8/PowerShell,PaulHigin/PowerShell,KarolKaczmarek/PowerShell,kmosher/PowerShell,KarolKaczmarek/PowerShell,daxian-dbw/PowerShell,jsoref/PowerShell,PaulHigin/PowerShell,PaulHigin/PowerShell,KarolKaczmarek/PowerShell,bmanikm/PowerShell,kmosher/PowerShell,jsoref/PowerShell,bingbing8/PowerShell,JamesWTruher/PowerShell-1,TravisEz13/PowerShell,jsoref/PowerShell,bingbing8/PowerShell,bingbing8/PowerShell,TravisEz13/PowerShell,bmanikm/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,TravisEz13/PowerShell,JamesWTruher/PowerShell-1,kmosher/PowerShell,TravisEz13/PowerShell,jsoref/PowerShell,KarolKaczmarek/PowerShell,bmanikm/PowerShell,jsoref/PowerShell