Strip newline from incoming SPTPS requests.

Most of the code doesn't care whether requests are terminated with a newline or
not, except that when requests are forwarded, it is assumed they do not have
one and a newline is added.  When a node using SPTPS receives a request from
another SPTPS-using node, and forwards it to a non-SPTPS-using node, this will
result in two consecutive newlines, which the latter node will see as an empty,
and thus invalid, request.