[krbdev.mit.edu #1448] krb4's vts_long() and vts_short() corrupt memory

[Alexandra Ellwood via RT]

krb4's vts_long() and vts_short() modify the passed in pointer so that
the caller can no longer free it -- they return a pointer to the middle
of the buffer.  Also, they both write to the beginning of the buffer
passed in, not appending data to the end like they should be doing.