Unit test fixes for AssertLockHeld / -DDEBUG_LOCKORDER

Unit tests would fail if compiled with -DDEBUG_LOCKORDER (AssertLockHeld()
would fail; AssertLockHeld() relies on the DEBUG_LOCKORDER code to keep
track of locks held).

Fixed by LOCK'ing the wallet mutex in the unit tests that manipulate the
wallet.

src/test/accounting_tests.cpp

@@ -34,6 +34,8 @@ BOOST_AUTO_TEST_CASE(acc_orderupgrade)
     CAccountingEntry ae;
     std::map<int64_t, CAccountingEntry> results;
 
+    LOCK(pwalletMain->cs_wallet);
+
     ae.strAccount = "";
     ae.nCreditDebit = 1;
     ae.nTime = 1333333333;