Monkey with JarUrlConnection to make it work when LANG unset

The problem all along has been in AsciiBytes, so the fix in
commit ce3aaf was just a stop gap for a system where multi-byte
characters are supported but the default encoding is not UTF-8 (e.g.
most Windows systems). The real solution is not to leave it to
chance and always pick an encoding for the JarEntry names (i.e.
in AsciiBytes).

Fixes gh-764

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarFileTests.java

@@ -91,6 +91,8 @@ public class JarFileTests {
 		URLClassLoader urlClassLoader = new URLClassLoader(new URL[] { jarUrl });
 		assertThat(urlClassLoader.getResource("special/\u00EB.dat"), notNullValue());
 		assertThat(urlClassLoader.getResource("d/9.dat"), notNullValue());
+		jarFile.close();
+		urlClassLoader.close();
 	}
 
 	@Test
@@ -133,6 +135,7 @@ public class JarFileTests {
 		URLClassLoader urlClassLoader = new URLClassLoader(
 				new URL[] { this.jarFile.getUrl() });
 		assertThat(urlClassLoader.getResource("special/\u00EB.dat"), notNullValue());
+		urlClassLoader.close();
 	}
 
 	@Test
@@ -365,5 +368,6 @@ public class JarFileTests {
 						jarEntry.getCertificates());
 			}
 		}
+		jarFile.close();
 	}
 }