Feature: Extra arg detection

- Commands that do not accept filters or modifications now generate an error
  when extra arguments are specified.

src/commands/CmdHelp.cpp

@@ -29,6 +29,7 @@
 #include <CmdHelp.h>
 #include <ViewText.h>
 #include <Context.h>
+#include <Filter.h>
 #include <i18n.h>
 #include <text.h>
 #include <util.h>
@@ -48,6 +49,12 @@ CmdHelp::CmdHelp ()
 ////////////////////////////////////////////////////////////////////////////////
 int CmdHelp::execute (std::string& output)
 {
+  Filter filter;
+  if (filter.hasFilter ())
+    throw std::string (STRING_ERROR_NO_FILTER);
+  if (filter.hasModifications ())
+    throw std::string (STRING_ERROR_NO_MODS);
+
   ViewText view;
   view.width (context.getWidth ());
   view.add (Column::factory ("string.left", ""));