print error details when asm or java failed to read class bytecode.

Seealso http://forums.xamarin.com/discussion/973/problems-binding-jar#latest

JavaArchive.java

@@ -94,6 +94,7 @@ void getPackages (HashMap<String, JavaPackage> packages, JarFile file)
 					}
 					pkg.addClass (new JavaClass (c, node));
 				} catch (Throwable t) {
+					t.printStackTrace ();
 					System.err.println ("warning J2X9001: Couldn't load class " + name + " : " + t);
 				}
 			}