upgraderepo: add a config option for parallel computation
The option is put to use to compute new copy tracing side data in parallel. It
use the multiprocessing module as it had the appropriate primitive for what we
needed. Gregory Szorc had concerned on windows so we disabled it there.
See inline comment for details on the parallel implementation.
{
// 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)
}