exthelper: reintroduce the ability to register revsets
I think this is what Yuya and Boris agreed on.[1] This happens *after* the
extsetup phase now (and after the _aftercallback notifications). But this is
trivial, mergeable between exthelper instances, and doesn't need to have the
extension name supplied when registering.
The test needed updating so that extsetup() takes a `ui` argument, as exthelper
isn't trying to be backward compatible with 1.3.1.
[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-December/125888.html
{
// 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)
}