[patch] enable ECDH auto functions based on feature defines, not on version number

Hello,

I recently tried to build my system with libressl instead of openssl.

In dovecot one issue that popped up was that libressl doesn't have the ECDH auto functions from openssl 1.0.2 beta versions. However as the #ifdef's in dovecot's code check for the openssl version and libressl's version numbers are higher the compilation fails there.

Attached is a patch that will change that checks. Instead of checking for the version number it checks for the availability of the feature itself (by checking for the define of SSL_CTRL_SET_ECDH_AUTO). This should make this check more robust and work independently of the version number of the used openssl instance.

cu,

Hanno Böck http://hboeck.de/

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