io::file needs to get expanded to be "fully functional"

[alexcrichton]

Missing pieces:

• symlink
• readlink
• hard links
• lstat
• file permission representation (argument to mkdir, argument to chmod, etc.)
• chmod
• chown
• truncate
• updating mtime/atime or other times on the file

Nominating, these need to get done for 1.0

[alexcrichton]

Un-nominating, parenting to a nominated metabug.

[alexcrichton]

This should be blocked on #10086