Surface AccountInUse to JSON RPC users so they know to retry the transaction

doc/json-rpc.md

@@ -168,6 +168,7 @@ events.
     * `Confirmed` - Transaction was successful
     * `SignatureNotFound` - Unknown transaction
     * `ProgramRuntimeError` - An error occurred in the program that processed this Transaction
+    * `AccountInUse` - Another Transaction had a write lock one of the Accounts specified in this Transaction.  The Transaction may succeed if retried
     * `GenericFailure` - Some other error occurred.  **Note**: In the future new Transaction statuses may be added to this list.  It's safe to assume that all new statuses will be more specific error conditions that previously presented as `GenericFailure`
 
 ##### Example:

src/bank.rs

@@ -302,6 +302,7 @@ impl Bank {
             if res[i] != Err(BankError::SignatureNotFound) {
                 let status = match res[i] {
                     Ok(_) => RpcSignatureStatus::Confirmed,
+                    Err(BankError::AccountInUse) => RpcSignatureStatus::AccountInUse,
                     Err(BankError::ProgramRuntimeError(_)) => {
                         RpcSignatureStatus::ProgramRuntimeError
                     }

src/rpc.rs

@@ -90,10 +90,11 @@ impl Metadata for Meta {}
 
 #[derive(Copy, Clone, PartialEq, Serialize, Debug)]
 pub enum RpcSignatureStatus {
+    AccountInUse,
     Confirmed,
-    SignatureNotFound,
-    ProgramRuntimeError,
     GenericFailure,
+    ProgramRuntimeError,
+    SignatureNotFound,
 }
 
 build_rpc_trait! {
@@ -157,6 +158,7 @@ impl RpcSol for RpcSolImpl {
         Ok(
             match meta.request_processor.get_signature_status(signature) {
                 Ok(_) => RpcSignatureStatus::Confirmed,
+                Err(BankError::AccountInUse) => RpcSignatureStatus::AccountInUse,
                 Err(BankError::ProgramRuntimeError(_)) => RpcSignatureStatus::ProgramRuntimeError,
                 Err(BankError::SignatureNotFound) => RpcSignatureStatus::SignatureNotFound,
                 Err(err) => {