revsets: add commonancestors revset
This is a method to reproduce "::x and ::y" such that a set can be sent
in. For instance, it'd be convenient to have "::heads()" work like this
but that already means "::x + ::y + ..." for each element in the
"heads()" set.
Therefore, we add the "commonancestors" method to mean "::x and ::y ..."
for each head in the given set.
{
// 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)
}