Convert a return code integer to a text string. This string can be
used to output a diagnostic message to the user.
PR29_SUCCESS
Successful operation. This value is guaranteed to
always be zero, the remaining ones are only guaranteed to hold
non-zero values, for logical comparison purposes.
PR29_PROBLEM
A problem sequence was encountered.
PR29_STRINGPREP_ERROR
The character set conversion failed (only
for pr29_8() and pr29_8z()).
RETURN VALUE
Returns a pointer to a statically allocated string
containing a description of the error with the return code rc.
