API: No mustposttoken error with $wgDebugAPI

$wgDebugAPI is supposed to be a way to quickly (and insecurely) test API
modules using GET where they'd normally require POST. But this purpose
is defeated if token handling still throws mustposttoken.

Change-Id: Iee2fb76da86bf0670f9816f24f68c611fa0728b1
Merge "API: No mustposttoken error with $wgDebugAPI"