configure: require OpenSSL >= 1.0.0

configure.ac

@@ -276,12 +276,21 @@ AS_IF([test "$with_openssl" != "no"],[
       LIBS="$save_LIBS"
     done
 
-    AS_IF([test "$with_openssl" = "no"],[
-      AC_MSG_ERROR([libcrypto (part of OpenSSL) is required])
-    ])
   ])
 ])
 
+AS_IF([test "$with_openssl" = "no"],[
+  AC_MSG_ERROR([OpenSSL library is required.])
+])
+
+AC_EGREP_CPP(openssl_version_ok,
+  [#include <openssl/crypto.h>
+   #if (OPENSSL_VERSION_NUMBER >= 0x1000000fL)
+   openssl_version_ok
+   #endif
+  ],[],[AC_MSG_ERROR([OpenSSL library version >= 1.0.0 is required.])]
+)
+
 AC_ARG_WITH(libidn, AC_HELP_STRING([--with-libidn=[DIR]],
     [Support IDN (needs GNU Libidn)]),
     libidn=$withval, libidn=yes)