copies: explicitly filter out existing file in graftcopies
The `graftcopies` function does something very strange (maybe even wrong), it
calls `_filter` with a pair of changeset that does not match the one used to
compute the copies informations.
We are about to do some rework of `_filter` to make it closer to its documented
intent and fix a couple of bug. This means some of the logic that only make
sense for graft need to go somewhere else. We add the extra filtering with
proper documentation to `graftcopies`.
Differential Revision: https://phab.mercurial-scm.org/D9802
{
// 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)
}