history.pushState should clear forward history

The spec currently says:

 "If the method invoked was the pushState() method:

  Remove from the session history any entries for the Document
  from the entry after the current entry up to the last entry
  in the session history that references the same Document
  object, if any. If the current entry is the last entry in
  the session history, or if there are no entries after the
  current entry that reference the same Document object, then
  no entries are removed."

I believe this behavior is undesirable.  Instead, pushState
should clear the entire forward history regardless of which
documents are involved.

A major use case for history.pushState is to eliminate the
dummy reference fragment navigations used by many apps to add
entries to session history without causing a "real" page load.
In that case, the app author wants to simulate a real page load,
and an important UI component of a real page load is that the
forward navigation button becomes disabled.

It seems strange when a "navigation" doesn't result in a
disabled forward button in the browser UI, so an app developer
may be unsatisfied using pushState in place of reference
fragment navigations.

Moreover, Firefox has implemented pushState in a manner that
clears the forward history.  The Mozilla folks seem to favor
their implementation.  There is also support in the WebKit
community for changing WebKit to match Firefox instead of what
is currently spec'd.