If dynamically-loadable ENGINEs are linked against a shared-library version

If dynamically-loadable ENGINEs are linked against a shared-library version
of libcrypto, then it is possible that when they are loaded they will share
the same static data as the loading application/library. This means it will
be too late to set memory/ERR/ex_data/[etc] callbacks, but entirely
unnecessary to try. This change puts a static variable in the core ENGINE
code (contained in libcrypto) and a function returning a pointer to it. If
the loaded ENGINE's return value from this function matches the loading
application/library's return value - they share static data. If they don't
match, the loaded ENGINE has its own copy of libcrypto's static data and so
the callbacks need to be set.

Also, although 0.9.7 hasn't been released yet, it's clear this will
introduce a binary incompatibility between dynamic ENGINEs built for 0.9.7
and 0.9.8 (though others probably exist already from EC_*** hooks and
what-not) - so the version control values are correspondingly bumped.