next_token() was supposed to be a reentrant replacement for strtok(),

next_token() was supposed to be a reentrant replacement for strtok(),
but the code suffered from bitrot and is not now reentrant. That means
we can get bizarre behaviour
i've fixed this by making next_token() reentrant and creating a
next_token_nr() that is a small non-reentrant wrapper for those lumps
of code (mostly smbclient) that have come to rely on the non-reentrant
behaviour