Replaced our old Patricia tree with Google's concurrent radix tree

This required some changes to the Prefix class to store a binary string
representation of the prefix to use as a key in the radix tree.

Also unrelated, bounds checking of the Prefix class has been improved and some
Prefix unit tests have been added.

Change-Id: I56f5b69346801ec70535ed470ae064b1fdf8cfdf
diff --git a/pom.xml b/pom.xml
index a39db9d..bced4a7 100644
--- a/pom.xml
+++ b/pom.xml
@@ -604,6 +604,11 @@
       </exclusions>
     </dependency>
     <dependency>
+      <groupId>com.googlecode.concurrent-trees</groupId>
+      <artifactId>concurrent-trees</artifactId>
+      <version>2.4.0</version>
+    </dependency>
+    <dependency>
       <groupId>org.apache.curator</groupId>
       <artifactId>curator-framework</artifactId>
       <version>2.4.1</version>