Merge #11726: Cleanups + nit fixes for walletdir PR

aac6b3f067 Update files.md for new wallets/ subdirectory (MeshCollider)
b67342906c Cleanups for walletdir PR (MeshCollider)

Pull request description:

  This addresses the remaining nits from https://github.com/bitcoin/bitcoin/pull/11466

  - Updates `doc/files.md` with respect to the new default wallet directory
  - Fixes @promag and @laanwj's error message nit, and Jonas' release notes nit
  - ~Addresses @laanwj's net-specific wallet subdirectory concern in the case that a walletdir is specified~
  - Changes the #includes from "" to <> style after #11651

Tree-SHA512: b86bf5fdc4de54c1b0f65b60a83af3cf82b35d216ce9c0de724803bfba6934796238b6c412659dcc29ae2e3e856d4eb97ae777c80f36f4089d8acecfddefe9aa

src/wallet/init.cpp

@@ -194,7 +194,10 @@ bool VerifyWallets()
     }
 
     if (gArgs.IsArgSet("-walletdir") && !fs::is_directory(GetWalletDir())) {
-        return InitError(strprintf(_("Error: Specified wallet directory \"%s\" does not exist."), gArgs.GetArg("-walletdir", "").c_str()));
+        if (fs::exists(fs::system_complete(gArgs.GetArg("-walletdir", "")))) {
+            return InitError(strprintf(_("Specified -walletdir \"%s\" is not a directory"), gArgs.GetArg("-walletdir", "").c_str()));
+        }
+        return InitError(strprintf(_("Specified -walletdir \"%s\" does not exist"), gArgs.GetArg("-walletdir", "").c_str()));
     }
 
     LogPrintf("Using wallet directory %s\n", GetWalletDir().string());

src/wallet/walletutil.cpp

@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include "wallet/walletutil.h"
+#include <wallet/walletutil.h>
 
 fs::path GetWalletDir()
 {

src/wallet/walletutil.h

@@ -5,7 +5,8 @@
 #ifndef BITCOIN_WALLET_UTIL_H
 #define BITCOIN_WALLET_UTIL_H
 
-#include "util.h"
+#include <chainparamsbase.h>
+#include <util.h>
 
 //! Get the path of the wallet directory.
 fs::path GetWalletDir();