more const in format detection

BaseImporter::SearchFileHeaderForToken() expected a pointer to a non-const token list. This was probably an oversight, as nobody would realistically expect the function to change the list. Furthermore, it prevented token lists from being compiled to read-only memory, in some cases even causing the compiler to generate thread-safe initialization.

The list is now const and all callers declare their token lists static const, thus compiling them to read-only memory.

code/AssetLib/MS3D/MS3DLoader.cpp

@@ -104,7 +104,7 @@ bool MS3DImporter::CanRead( const std::string& pFile, IOSystem* pIOHandler, bool
         if (!pIOHandler) {
             return true;
         }
-        const char* tokens[] = {"MS3D000000"};
+        static const char * const tokens[] = {"MS3D000000"};
         return SearchFileHeaderForToken(pIOHandler,pFile,tokens,1);
     }
     return false;