Polish timeout handling

The abs() function may not be needed, and the !reverse condition is
really hard to follow. Bonus point, the way the if statement is broken
doesn't comply with our code style (it came from stud).

Refs #297
Refs #298

src/hitch.c

@@ -461,8 +461,9 @@ handle_shcupd(struct ev_loop *loop, ev_io *w, int revents)
 		/* drop too unsync updates */
 		r -= sizeof(uint32_t);
 		encdate = *((uint32_t *)&msg[r]);
-		if (!(abs((int)(int32_t)now - ntohl(encdate))
-			< SSL_CTX_get_timeout(default_ctx->ctx)))
+		assert(now >= ntohl(encdate));
+		if ((now - ntohl(encdate)) >=
+		    SSL_CTX_get_timeout(default_ctx->ctx))
 			continue;
 
 		shctx_sess_add(msg, r, now);