dirstate: simplify the invalidation management on context exit
Since the `invalidate` call will directly reset the `_invalidated_context` attribut, we can simplify the code.
In the same go, we move most of the logic out of the `finally` clause. It seems
cleaner and safer. If we are handling an exception, we don't need the `write`
code anyway.
{
// 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)
}