Fix #2915
Now creates a file symlink to a file target and to an non-existent target, and a directory symlink to a directory target.

Creating Links with New-Item

The New-Item cmdlet allows for creating file system links.
In general, New-Item can create four types of links:

• Hard Link
  • Created when -ItemType is HardLink
• Symbolic Link
  • Created when -ItemType is SymbolicLink and either the target exists and is a file, or the target does not exist
    • In Windows, if the target is a directory then New-Item -ItemType Symbolic Link will create a directory symbolic link, not a "plain" symbolic link.
    • In Linux and OS X, New-Item -ItemType Symbolic Link will always create a "plain" symbolic link, regardless of whether the target is a file or directory, or whether the target exists or not.
  • In Windows, elevated privileges are required to create a symbolic link.
• Directory Symbolic Link
  • Created when -ItemType is SymbolicLink and the target exists and is a directory
  • Supported only on NTFS file system
  • In Windows, elevated privileges are required to create a directory symbolic link.
  • In Linux and OS X, New-Item will not create a directory symbolic link, even on an NTFS volume.
• Directory Junction
  • Supported only on NTFS file system
  • In Linux and OS X, New-Item will not create a directory junction, even on an NTFS volume.
    • Currently, New-Item will begin to create the junction by creating the link directory. When the attempt to turn the newly-created directory into a junction fails, New-Item will delete the new directory and silently fail.

The following table shows the types of links and targets the New-Item cmdlet can create on Windows:

Link Type / Target	Existing File	Existing Directory	Non-Existent	"Plain" Symbolic Link	Directory Symbolic Link	Directory Junction
Hard Link	Yes	No	No	Yes	No	No
"Plain" Symbolic Link	Yes	No1	Yes	Yes	No1	No1
Directory Symbolic Link	No1	Yes	No1	No1	Yes	Yes
Directory Junction	No	Yes	No	No	Yes	Yes

1 While the NTFS file system and the Windows operating system support "plain" symbolic links to existing directories and *directory* symbolic links to files and to non-existent items, the `New-Item` cmdlet cannot create them.

The following table shows the types of links and targets the New-Item cmdlet can create on Linux and OS X:

Link Type / Target	Existing File	Existing Directory	Non-Existent	"Plain" Symbolic Link	Directory Symbolic Link	Directory Junction
Hard Link	Yes	No	No	Yes	No	No
"Plain" Symbolic Link	Yes	Yes	Yes	Yes	No	No
Directory Symbolic Link2	No	No	No	No	No	No
Directory Junction2	No	No	No	No	No	No

2 The Linux and OS X operating systems do not support *directory* symbolic links or directory junctions.