I2CP: Take 2 of fix, so a newly created session

isn't destroyed and immediately replaced by i2ptunnel,
which caused dup shared clients in a race at startup;
Clarify session exception text if not open

router/java/src/net/i2p/router/RouterVersion.java

@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Monotone";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 29;
+    public final static long BUILD = 30;
 
     /** for example "-test" */
     public final static String EXTRA = "-rc";