Make OpenSSL an hcrypto backend proper

This adds a new backend for libhcrypto: the OpenSSL backend.

Now libhcrypto has these backends:

 - hcrypto itself (i.e., the algorithms coded in lib/hcrypto)
 - Common Crypto (OS X)
 - PKCS#11 (specifically for Solaris, but not Solaris-specific)
 - Windows CNG (Windows)
 - OpenSSL (generic)

The ./configure --with-openssl=... option no longer disables the use of
hcrypto.  Instead it enables the use of OpenSSL as a (and the default)
backend in libhcrypto.  The libhcrypto framework is now always used.

OpenSSL should no longer be used directly within Heimdal, except in the
OpenSSL hcrypto backend itself, and files where elliptic curve (EC)
crypto is needed.

Because libhcrypto's EC support is incomplete, we can only use OpenSSL
for EC.  Currently that means separating all EC-using code so that it
does not use hcrypto, thus the libhx509/hxtool and PKINIT EC code has
been moved out of the files it used to be in.

include/config.h.w32

@@ -1,5 +1,5 @@
 /***********************************************************************
- * Copyright (c) 2009, Secure Endpoints Inc.
+ * Copyright (c) 2009-2016, Secure Endpoints Inc.
  * All rights reserved.
  * 
  * Redistribution and use in source and binary forms, with or without
@@ -652,8 +652,8 @@ static const char *const rcsid[] = { (const char *)rcsid, "@(#)" msg }
 /* Define to 1 if you have the `openpty' function. */
 /* #define HAVE_OPENPTY 1 */
 
-/* define to use openssl's libcrypto */
-/* #undef HAVE_OPENSSL */
+/* define to 1 to use openssl's libcrypto as a (default) backend for libhcrypto */
+/* #undef HAVE_HCRYPTO_W_OPENSSL */
 
 /* Define to enable basic OSF C2 support. */
 /* #undef HAVE_OSFC2 */