Use nresource=[native jar] to add contents of resource to java.library.path

This feature makes use of the current caching system for "code" jars. Resources marked by nresource are copied to specific cache directories, unpacked, and then the caches are added to the applications java.library.path. This "native" cache is cleaned according to "cache_retention_days", similar to the code cache.

core/src/test/java/com/threerings/getdown/classpath/ClassPathsTest.java

@@ -46,10 +46,10 @@ public class ClassPathsTest
         when(_application.getCodeCacheRetentionDays()).thenReturn(1);
 
         Path firstCachedJarFile = _appdir.getRoot().toPath().
-            resolve(ClassPaths.CACHE_DIR).resolve("fi").resolve("first.jar");
+            resolve(Application.CACHE_DIR + "/code").resolve("fi").resolve("first.jar");
 
         Path secondCachedJarFile = _appdir.getRoot().toPath().
-            resolve(ClassPaths.CACHE_DIR).resolve("se").resolve("second.jar");
+            resolve(Application.CACHE_DIR + "/code").resolve("se").resolve("second.jar");
 
         String expectedClassPath = firstCachedJarFile.toAbsolutePath() + File.pathSeparator +
             secondCachedJarFile.toAbsolutePath();