Fix back button not exiting VE
When you clicked the Back button in the browser, the URL
in the address bar would change (removing veaction=edit),
but we would not go back to read mode. This was broken
by 5c0c11753 almost a month ago but apparently no one noticed.
This is because 5c0c11753 moved the pushState() calls to
be earlier (in init init), making the replaceState() call
in the ViewPageTarget constructor (which is there
specifically for this bug) run too late in those cases.
The simplest way to fix this is to duplicate these replaceState()
calls before the pushState() calls in init init.
I feel a bit bad about copying code, but not very bad
because the code I'm copying already has a FIXME comment
about how there should be a better way :P