rust-dirstatemap: add `set_cached_mtime` helper method
This will help remove the `get_or_insert` method, which is dangerous because it
does not take the `DirstateMap` counters into account
Differential Revision: https://phab.mercurial-scm.org/D12526
{
// 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)
}