upgrade: update only requirements if we can
Upgrade operations which involves just upgrading requirements earlier used to go
through whole revlog cloning business.
Now we just upgrade the requirement and skip the cloning part.
Differential Revision: https://phab.mercurial-scm.org/D9775
{
// 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)
}