Cothread beyond version 2.18.2 can break long string handling in affected servers

Commit 1ec3579761d4b1901bf65d0c1e58b063191273df of PR #32 changes the behaviour of puts to "long strings" (arrays of char) so that a trailing null is no longer sent. This makes the length of the string (as reported by `.NORD`) truthful, but unfortunately can trigger bugs in string length calculations in certain servers.

Either cothread should unconditionally append an extra null (making all strings one character longer than is truthful) or this could be done conditionally on something like an environment variable.