Inconsistent treatment of globals with mangle_properties()

[AshleyScirra]

mangle_properties() will mangle properties on the global object, whereas the rest of UglifyJS does not modify globals. This inconsistency breaks scripts which create globals like so:

window.Foo = {};
Foo.bar = 1;

// is mangled to:
window.q = {}; // mangled property
Foo.r = 1;  // unmangled global

There should be a way to make mangle_properties avoid mangling properties where the left side of the dot is a well-known global alias, i.e. window, self, global.

[AshleyScirra]

This is actually pretty complicated. For example localforage does something like this:

(function (e)
{
    e.localforage = {...};
})(window);

It's probably pretty complicated to figure out that it's a global reference there... I guess maybe the solution is just to reserve the property name localforage :-\