on any access

Archive engine for 5.1 (and latter) version uses a modified 
version of zlib (azlib). These two version are incompatible
so a proper upgrade is needed before tables created in 5.0 
can be used reliable.

This upgrade can be performed using repair. But due to lack 
of test its risky to allow upgrade for now. This patch addresses
only the crashing issue. Any attempt to repair will be blocked.

Eventually repair can be allowed to run through (which will also
cause an upgrade from older version to newer) but only after a 
thorough testing.