Don't close associated file descriptors in the closem()
tidy up function as they should remain visible to external
processes. Override if about to exit.
Unit test for the failing case: note this relies on the
existence of /proc/self/fd or equivalent.
Shell functions are strictly ASCII for maximum portability.
Other files within the distribution may contain UTF-8 characters.
Exception for test files: where they need single character input
with the top bit set, ISO-8859-X is used (X doesn't matter as
we don't need the Euro).
