openssl: assume engine support in 1.0.0 or later

openssl: assume engine support in 1.0.0 or later

Commit 38203f1585da changed engine detection to be version-based,
with a baseline of openssl 1.0.1. This does in fact break builds
with openssl 1.0.0, which has engine support - the configure script
detects that ENGINE_cleanup() is available - but <openssl/engine.h>
doesn't get included to declare it.

According to upstream documentation, engine support was added to
mainstream openssl builds as of version 0.9.7:
https://github.com/openssl/openssl/blob/master/README.ENGINE

This commit drops the version test down to 1.0.0 as version 1.0.0d
is the oldest version I have to test with.

Closes #2732