On AllegroCL Slimv was attempting to call frame-call when expanding a frame in backtrace. SLIME responded with a not implemented response.
This change prevents the call.
A prior commit (on 3-27-12) seems to indicate that slimv should not perform this call on lisps that don't implement it, but only actually stops it for clisp. I believe the only lisps that actually implement frame-call are SBCL and CCL, so perhaps this could be written differently. My change is the minimum change to get allegro functional.