- (djm) [configure.ac] Check OpenSSL version is supported at configure time;
   suggested by Kevin Brott
 - (djm) [Makefile.in] refer to libtest_helper.a by explicit path rather than
   -L/-l; fixes linking problems on some platforms
 - (djm) [sshkey.h] Fix compilation when OpenSSL lacks ECC
 - (djm) [contrib/cygwin/README] Correct build instructions; from Corinna