4167874: URL-downloaded jar files can consume all available file descriptors
Summary: added close method to URLClassLoader
Reviewed-by: alanb
test1 and test2 contain two different implementations of the sameclasses. They are compiled and placed into two different target directoriesand two jar files test1.jar and test2.jar.The same class is in both jars/directories, but returns a different resultfrom the TestClass.getValue() method. The test does the following1. copy test1.jar to a working directory and call it test.jar2. load class and invoke method (checking result)3. close the loader4. delete test.jar (check delete succeeds)5. copy test2.jar to same dir and repeat the test6. The two tests are then repeated by copying the directories test1 and test2.The loader also includes a http:// URL in its search path and a httpserver is used to serve the required class.serverRoot is used as the root directory for the http server.