Security framework.

Security callback: selects which parameters are permitted including
sensible defaults based on bits of security.

The "parameters" which can be selected include: ciphersuites,
curves, key sizes, certificate signature algorithms, supported
signature algorithms, DH parameters, SSL/TLS version, session tickets
and compression.

In some cases prohibiting the use of a parameters will mean they are
not advertised to the peer: for example cipher suites and ECC curves.
In other cases it will abort the handshake: e.g DH parameters or the
peer key size.

Documentation to follow...

ssl/tls1.h

@@ -157,6 +157,11 @@
 extern "C" {
 #endif
 
+/* Default security level if not overriden at config time */
+#ifndef OPENSSL_TLS_SECURITY_LEVEL
+#define OPENSSL_TLS_SECURITY_LEVEL 1
+#endif
+
 #define TLS1_ALLOW_EXPERIMENTAL_CIPHERSUITES	0
 
 #define TLS1_2_VERSION			0x0303