1.1.15: will be tagged as "sbcl-1.1.15"
Fix concurrently doing TYPEP and redefining the class it checks.

Grabbing the world lock in %FORCE-CACHE-FLUSHES prevents
CLASSOID-TYPEP from messing things up.

Fixes lp#1272742.
Optimize functions calling wrapper-of.

SB-PCL::WRAPPER-OF is just a synonym for LAYOUT-OF and it's declared
inline, but it's used before it's defined, which prevents inlining.
Move it before the first use. That makes some operations a bit faster.