revset: prevent infinite recursion on pypy as explained in the commit, __len__ cannot do [x for x in self] because that can potentially call __len__ again, causing infinite recursion

pypy: fix doctests for pypy optimizations PyPy would sometime call __len__ at points where it things preallocating the container makes sense. Change the doctests so they're using generator expressions and not list comprehensions

largefiles: replace invocation of os.path module by vfs in reposetup.py This commit is part of bigger effort described in 'Windows UTF-8' plan.