if sgh-mpm-context is not available in conf, alias the auto case inside the engine

src/detect-engine.c

@@ -238,8 +238,15 @@ static uint8_t DetectEngineCtxLoadConf(DetectEngineCtx *de_ctx) {
         }
     } else {
         SCLogInfo("You have not supplied a value for "
-                  "detect-engine.sgh-mpm-context. Using default value of \"full\"");
-        de_ctx->sgh_mpm_context = ENGINE_SGH_MPM_FACTORY_CONTEXT_FULL;
+                  "detect-engine.sgh-mpm-context. Using default value of \"auto\"");
+        if (de_ctx->mpm_matcher == MPM_AC || de_ctx->mpm_matcher == MPM_AC_GFBS)
+            de_ctx->sgh_mpm_context = ENGINE_SGH_MPM_FACTORY_CONTEXT_SINGLE;
+        else
+            de_ctx->sgh_mpm_context = ENGINE_SGH_MPM_FACTORY_CONTEXT_FULL;
+
+        /* someday when our engine turns intelligent we will actualy support this
+         * option internally */
+        //de_ctx->sgh_mpm_context = ENGINE_SGH_MPM_FACTORY_CONTEXT_AUTO;
     }