Fix fixing of std::string object names

Comparing two fixed std::strings would have equal C strings but comparing
with operator== they would be different. This was a result of the string
modification done by fix_object_name.

Converted the internal header into a C++ header, added std::string
overload and fixed use of the function.

server/modules/routing/binlogrouter/test/testbinlog.cc

@@ -42,7 +42,7 @@
 #include <maxscale/alloc.h>
 #include <maxscale/utils.hh>
 #include "../../../../core/internal/modules.h"
-#include "../../../../core/internal/config.h"
+#include "../../../../core/internal/config.hh"
 
 #include <maxscale/protocol/mysql.h>
 #include <ini.h>