Transaction: do a better job at showing invalid scriptSigs in toString()

Previously, it was just showing an exception message. This is improved
as follows:

- if an input scriptSig cannot be parsed, the raw bytes are shown instead
- also, the input value is shown if available
- for the coinbase input, which may be arbitrary bytes, the exception message
  is suppressed

core/src/main/java/org/bitcoinj/core/Transaction.java

@@ -810,7 +810,15 @@ public class Transaction extends BaseMessage {
                         s.append('\n');
                     }
                 } catch (Exception e) {
-                    s.append("[exception: ").append(e.getMessage()).append("]\n");
+                    s.append(ByteUtils.formatHex(getInput(0).getScriptBytes()));
+                    if (!isCoinBase()) {
+                        final Coin value = in.getValue();
+                        if (value != null)
+                            s.append("  ").append(value.toFriendlyString());
+                        s.append('\n');
+                        s.append(indent).append("        exception: ").append(e.getMessage());
+                    }
+                    s.append('\n');
                 }
             }
         } else {

core/src/test/java/org/bitcoinj/core/TransactionTest.java

@@ -515,7 +515,7 @@ public class TransactionTest {
         };
 
         tx.addInput(ti);
-        assertTrue(tx.toString().contains("[exception: "));
+        assertTrue(tx.toString().contains("exception: "));
     }
 
     @Test