* Mono.Posix.dll.sources: Add UnixDriveInfo and UnixPath.

  * Mono.Posix.dll.sources: Add UnixDriveInfo and UnixPath.
  * CdeclFunctions.cs: Correct the comments for AMD64
  * UnixDirectoryInfo.cs: override Name; add Parent & Root properties;
    Correct Path usage (s/Path/FullPath/g).
  * UnixDriveInfo.cs: Added.  Based on .NET 2.0 System.IO.DriveInfo docs,
    provides statvfs(2) and getfsfile(3) information about a mounted volume.
    GetDrives() wraps getfsent(3), thus parsing /etc/fstab.
  * UnixFile.cs: Use UnixConver.ToOpenFlags, deleting the local version.
  * UnixFileInfo.cs: Use UnixConver.ToOpenFlags, deleting the local version;
    override Name; add DirectoryName and Directory properties;
  * UnixFileSystemInfo.cs: Make more .NET-like, using FullPath and
    OriginalPath protected members, abstract Name property; Add
    CreateSymbolicLink; Remove ReadLink (it's now
    UnixSymbolicLinkInfo.Contents); Use lstat(2) for Create(string), so we
    properly detect Symbolic Links.
  * UnixPath.cs: Added; Path manipulation utility functions.
  * UnixSymbolicLinkInfo.cs:
    - Seal the class;
    - override new abstract member Name;
    - rename ReadLink to ContentsPath (and Contents) properties
      (why "Contents"?  Because readlink(2) says "readlink places the
      contents of the symbolic link in the buffer...")
    - Add CreateSymbolicLinkTo(), which creates a symlink to the specified
      "normal" file

svn path=/trunk/mcs/; revision=38140