Rename db log category to walletdb (like coindb)

Deprecate (but still accept) '-debug=db'.

src/logging.cpp

@@ -95,7 +95,15 @@ void BCLog::Logger::EnableCategory(BCLog::LogFlags flag)
 bool BCLog::Logger::EnableCategory(const std::string& str)
 {
     BCLog::LogFlags flag;
-    if (!GetLogCategory(flag, str)) return false;
+    if (!GetLogCategory(flag, str)) {
+        if (str == "db") {
+            // DEPRECATION: Added in 0.20, should start returning an error in 0.21
+            LogPrintf("Warning: logging category 'db' is deprecated, use 'walletdb' instead\n");
+            EnableCategory(BCLog::DB);
+            return true;
+        }
+        return false;
+    }
     EnableCategory(flag);
     return true;
 }
@@ -139,7 +147,7 @@ const CLogCategoryDesc LogCategories[] =
     {BCLog::HTTP, "http"},
     {BCLog::BENCH, "bench"},
     {BCLog::ZMQ, "zmq"},
-    {BCLog::DB, "db"},
+    {BCLog::DB, "walletdb"},
     {BCLog::RPC, "rpc"},
     {BCLog::ESTIMATEFEE, "estimatefee"},
     {BCLog::ADDRMAN, "addrman"},