util: Report parse errors in configuration file

Report errors while parsing the configuration file, instead of silently
ignoring them.

    $ src/bitcoind -regtest
    Error reading configuration file: parse error on line 22: nodebuglogfile, if you intended to specify a negated option, use nodebuglogfile=1 instead
    $ src/bitcoind -regtest
    Error reading configuration file: parse error on line 22: sdafsdfafs
    $ src/bitcoind -regtest
    Error reading configuration file: parse error on line 24: -nodebuglogfile=1, options in the configuration file must be specified without leading -

src/util.cpp

@@ -812,11 +812,11 @@ static std::string TrimString(const std::string& str, const std::string& pattern
     return str.substr(front, end - front + 1);
 }
 
-static std::vector<std::pair<std::string, std::string>> GetConfigOptions(std::istream& stream)
+static bool GetConfigOptions(std::istream& stream, std::string& error, std::vector<std::pair<std::string, std::string>> &options)
 {
-    std::vector<std::pair<std::string, std::string>> options;
     std::string str, prefix;
     std::string::size_type pos;
+    int linenr = 1;
     while (std::getline(stream, str)) {
         if ((pos = str.find('#')) != std::string::npos) {
             str = str.substr(0, pos);
@@ -826,21 +826,34 @@ static std::vector<std::pair<std::string, std::string>> GetConfigOptions(std::is
         if (!str.empty()) {
             if (*str.begin() == '[' && *str.rbegin() == ']') {
                 prefix = str.substr(1, str.size() - 2) + '.';
+            } else if (*str.begin() == '-') {
+                error = strprintf("parse error on line %i: %s, options in configuration file must be specified without leading -", linenr, str);
+                return false;
             } else if ((pos = str.find('=')) != std::string::npos) {
                 std::string name = prefix + TrimString(str.substr(0, pos), pattern);
                 std::string value = TrimString(str.substr(pos + 1), pattern);
                 options.emplace_back(name, value);
+            } else {
+                error = strprintf("parse error on line %i: %s", linenr, str);
+                if (str.size() >= 2 && str.substr(0, 2) == "no") {
+                    error += strprintf(", if you intended to specify a negated option, use %s=1 instead", str);
+                }
+                return false;
             }
         }
+        ++linenr;
     }
-    return options;
+    return true;
 }
 
 bool ArgsManager::ReadConfigStream(std::istream& stream, std::string& error, bool ignore_invalid_keys)
 {
     LOCK(cs_args);
-
+    std::vector<std::pair<std::string, std::string>> options;
-    for (const std::pair<std::string, std::string>& option : GetConfigOptions(stream)) {
+    if (!GetConfigOptions(stream, error, options)) {
+        return false;
+    }
+    for (const std::pair<std::string, std::string>& option : options) {
         std::string strKey = std::string("-") + option.first;
         std::string strValue = option.second;