copies: extract function for deciding whether to use changeset-centric algos
We'll eventually have a "experimental.copies.read-from=changeset-only"
option too and I don't want to spread the logic for determining if we
should use changeset-centric of filelog-centric algorithms.
Differential Revision: https://phab.mercurial-scm.org/D6163
{
// 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)
}