Support for FatJars and executable WARs created by Spring-Boot

I've included the Patch from Slavus (see his Pull-Request) and added a break to prevent further handling the JAR URL by the original JarUrlProcolHandler. In my case (executable WAR created by spring-boot) a FileNotFoundException is thrown when the JarFile is created. 
This locator works fine now in spring-boot environments.

This solves issue #53 and includes the changes of the pull request of issue #54.