Revert "Only load error strings once"
Revert "Only load error strings once"

This reverts commit 2652c1b1e9cc90fab239a4a589d2aead13a12844.

Neiter this one nor the internal OpenSSL implementation are
sufficient to deal with engine unloading described in #264.

OpenSC/libp11,mouse07410/libp11,mtrojnar/libp11,mtrojnar/libp11,mouse07410/libp11,dengert/libp11,OpenSC/libp11,dengert/libp11