raise minimum TLS version to 1.2 (current maximum)

Index: src/config/local/crypto.h
--- src/config/local/crypto.h.orig
+++ src/config/local/crypto.h
@@ -0,0 +1,2 @@
+#undef  TLS_VERSION_MIN
+#define TLS_VERSION_MIN TLS_VERSION_TLS_1_2
