largefiles: refactor _usercachedir() to allow reuse with lfs
Largefiles puts everything into a flat directory, while lfs divides files up by
creating subdirectories consisting of the first two characters of the hash.
Therefore, pointing at the largefiles cache won't work.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}