Function escapeShellArg

Properly escape arguments containing spaces for the command shell, if necessary.

const(string) escapeShellArg (
  const(string) str
);

string escapeShellArg (
  Path path
);

Although Path doesn't strictly need this (since Path.toString automatically calls this anyway), an overload of escapeShellArg which accepts a Path is provided for the sake of generic code.