Re-apply changes

core/src/main/kotlin/com/r3corda/core/Utils.kt

@@ -146,6 +146,14 @@ class ThreadBox<T>(content: T, val lock: Lock = ReentrantLock()) {
     inline fun <R> locked(body: T.() -> R): R = lock.withLock { body(content) }
 }
 
+/**
+ * This represents a transient exception or condition that might no longer be thrown if the operation is re-run or called
+ * again.
+ *
+ * We avoid the use of the word transient here to hopefully reduce confusion with the term in relation to (Java) serialization.
+ */
+abstract class RetryableException(message: String) : Exception(message)
+
 /**
  * A simple wrapper that enables the use of Kotlin's "val x by TransientProperty { ... }" syntax. Such a property
  * will not be serialized to disk, and if it's missing (or the first time it's accessed), the initializer will be