Remove double-dash parameters from mapArgs

Should be merged after pull request bitcoin#4281
("Add `-version` option to get just the version bitcoin#4281"),
because is changed "--help" to "-help".

Checked that grep of 'mapArgs.count("--' returned only
three places that are fixed by pull request bitcoin#4281.

src/util.cpp

@@ -459,6 +459,7 @@ void ParseParameters(int argc, const char* const argv[])
 {
     mapArgs.clear();
     mapMultiArgs.clear();
+
     for (int i = 1; i < argc; i++)
     {
         std::string str(argv[i]);
@@ -474,29 +475,24 @@ void ParseParameters(int argc, const char* const argv[])
         if (boost::algorithm::starts_with(str, "/"))
             str = "-" + str.substr(1);
 #endif
+
         if (str[0] != '-')
             break;
 
+        // Interpret --foo as -foo.
+        // If both --foo and -foo are set, the last takes effect.
+        if (str.length() > 1 && str[1] == '-')
+            str = str.substr(1);
+
         mapArgs[str] = strValue;
         mapMultiArgs[str].push_back(strValue);
     }
 
     // New 0.6 features:
     BOOST_FOREACH(const PAIRTYPE(string,string)& entry, mapArgs)
     {
-        string name = entry.first;
-
-        //  interpret --foo as -foo (as long as both are not set)
-        if (name.find("--") == 0)
-        {
-            std::string singleDash(name.begin()+1, name.end());
-            if (mapArgs.count(singleDash) == 0)
-                mapArgs[singleDash] = entry.second;
-            name = singleDash;
-        }
-
         // interpret -nofoo as -foo=0 (and -nofoo=0 as -foo=1) as long as -foo not set
-        InterpretNegativeSetting(name, mapArgs);
+        InterpretNegativeSetting(entry.first, mapArgs);
     }
 }