getExt, getName and join doesn't support Windows's altsep, look at pull for D2's phobos:
https://github.com/D-Programming-Language/phobos/pull/63

Confusing (for me) behaviour of functions:

1. isabs - from
http://msdn.microsoft.com/en-us/library/aa365247%28v=vs.85%29.aspx
: "A single backslash, for example, "\directory" or "\file.txt". This is also referred to as an absolute path." and in .NET Framework Path.IsPathRooted returns true for such case, e.g. But I agree with phobos's way, and this behaviour is clearly written in documentation. Have it your way. But it affects next function.

2. join - if second path is "drive relative rooted":
assert( join(`a`, `\b`) == `\b` ); //good (like .NET Framework)
assert( join(`c:a`, `\b`) == `c:a\b` ); //why not `c:\b`?
assert( join(`c:\a`, `\b`) == `c:\a\b` ); //why not `c:\b`?

.NET Framework's Path.Combine for all cases shows `\b` (because `\b` is rooted for it).

Possible solutions:
1. We don't want to know about Microsoft's stupid "drive relative rooted" paths, let it be so:
assert( join(`a`, `\b`) == `a\b` );
assert( join(`c:a`, `\b`) == `c:a\b` );
assert( join(`c:\a`, `\b`) == `c:\a\b` );

2. We know about it:
assert( join(`a`, `\b`) == `\b` );
assert( join(`c:a`, `\b`) == `c:\b` );
assert( join(`c:\a`, `\b`) == `c:\b` );