support --without-openssl at configure time

Disables and removes dependency on OpenSSL. Many features don't
work and the set of crypto options is greatly restricted. This
will only work on system with native arc4random or /dev/urandom.

Considered highly experimental for now.
diff --git a/monitor_wrap.c b/monitor_wrap.c
index f4e11c9..b0dbb3f 100644
--- a/monitor_wrap.c
+++ b/monitor_wrap.c
@@ -151,8 +151,10 @@
 	debug3("%s entering", __func__);
 
 	if (atomicio(read, sock, buf, sizeof(buf)) != sizeof(buf)) {
-		if (errno == EPIPE)
+		if (errno == EPIPE) {
+			error("%s: socket closed", __func__);
 			cleanup_exit(255);
+		}
 		fatal("%s: read: %s", __func__, strerror(errno));
 	}
 	msg_len = get_u32(buf);