revset: drop magic of fullreposet membership test (issue4682) This patch partially backs out d2de20e1451f and adds an alternative workaround to functions that evaluate "null" and "wdir()". Because the new workaround is incomplete, "first(null)" and "min(null)" don't work as expected. But they were not usable until 3.4 and "null" isn't commonly used, we can postpone a complete fix for 3.5. The issue4682 was caused because "branch(default)" is evaluated to "<filteredset <fullreposet>>", keeping fullreposet magic. The next patch will fix crash on "branch(null)", but without this patch, it would make "null in <branch(default)>" be True, which means "children(branch(default))" would return all revisions but merge (p2 != null). I believe the right fix is to stop propagating fullreposet magic on filter(), but it wouldn't fit to stable release. Also, we should discuss how to handle "null" and "wdir()" in revset before.