new tools VTK2TIN, TIN2VTK

as titled
this is only true if the file open operation failed. for all other errors (i.e. while reading the file) errors are only stored in the vector.
personally, i would simply output errors in the TIN-interface when they occur (the interface exits after errors anyway) and would skip the error-vector completely. but maybe there is a good reason why this is included that i don't see.
again, if you did things I commented on purpose, just say so...