Return from RPC methods original transaction v value

[gumb0]

Fixes the problem mentioned in #4999 (comment)

cc @winsvega

[halfalicious]

Looks like a new intermittent test failure (I've seen this before in one of my PRs but the test passed on re-run):

"737/768 Test #740: JsonRpcSuite/jsonrpc_setMining ........................................................................................***Failed    0.32 sec
Running tests using path: "/Users/distiller/project/test/jsontests"
Assertion failed: (h), function syncBlockQueue, file /Users/distiller/project/libethereum/Client.cpp, line 383.
Running 1 test case...
Test Case "jsonrpc_setMining": 
unknown location:0: fatal error: in "JsonRpcSuite/jsonrpc_setMining": signal: SIGABRT (application abort requested)
/Users/distiller/project/test/unittests/libweb3jsonrpc/jsonrpc.cpp:242: last checkpoint: "jsonrpc_setMining" fixture dtor

*** 1 failure is detected (6 failures are expected) in the test module "Master Test Suite"