[phobos] Platform consistency of std.file

[Lars Tandle Kyllingstad]

Quick question:  Should the functions in std.file have a common "Phobos
behaviour" across platforms, or should they have the default/expected
behaviour for each platform?

Example:
std.file.copy() for Windows uses the Windows API, and thus I assume it
behaves in the way Windows users expect.  On POSIX, however, it uses a
home-brewed implementation, which does not behave completely like the
'cp' command.  (See bug 3862, which is what got me thinking about this.)

-Lars