revlog: do not call Rust code if the index is not compatible with it
This will avoid hitting the TypeError we defined in the previous changesets.
This is the simplest fix but not the most elegant.
Ideally we would teach the Rust code to use any kind of revlog. However this is
an adventure for another time.
Differential Revision: https://phab.mercurial-scm.org/D10666
{
// 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)
}