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/Ply/PlyLoader.cpp

@@ -111,7 +111,7 @@ bool PLYImporter::CanRead(const std::string &pFile, IOSystem *pIOHandler, bool c
         if (!pIOHandler) {
             return true;
         }
-        static const char *tokens[] = {
+        static const char * const tokens[] = {
             "ply"
         };
         return SearchFileHeaderForToken(pIOHandler, pFile, tokens, 1);