JAVA: Add minimum Java version to POM file. Fix issue 26.

java/pom.xml

@@ -125,6 +125,15 @@
           </tagBase>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>2.3.2</version>
+        <configuration>
+          <source>1.5</source>
+          <target>1.5</target>
+        </configuration>
+      </plugin>
     </plugins>
   </build>