py3: use dict.update() instead of constructing lists and adding them
dict.items() returned a list on Python 2 and whereas on Python 3 it returns a
view object. So we required a work around. Using dict.update() is better then
constructing lists as it should save us on gc churns.
#require execbit
$ hg init repo
$ cd repo
$ echo foo > foo
$ chmod 644 foo
$ hg ci -qAm '644'
$ chmod 755 foo
$ hg ci -qAm '755'
reverting to rev 0
$ hg revert -a -r 0
reverting foo
$ hg st
M foo
$ hg diff --git
diff --git a/foo b/foo
old mode 100755
new mode 100644
$ cd ..