let user select wallet file with -wallet=foo.dat

use std::string instead of psz for WalletFile

only allow wallets within $DATADIR

Use strWalletFile in salvage/recover

fix: remove unused variable pszWalletFile

move strWalletFile to init.h/init.cpp

avoid conversion of strWalletfile to c-string

src/qt/optionsmodel.cpp

@@ -89,7 +89,7 @@ bool OptionsModel::Upgrade()
     settings.setValue("bImportFinished", true);
 
     // Move settings from old wallet.dat (if any):
-    CWalletDB walletdb("wallet.dat");
+    CWalletDB walletdb(strWalletFile);
 
     QList<QString> intOptions;
     intOptions << "nDisplayUnit" << "nTransactionFee";