Check the input to see if it may be normalized into different
strings by different NFKC implementations, due to an anomaly in the
Returns the Pr29_rc value PR29_SUCCESS on success,
and PR29_PROBLEM if the input sequence is a "problem sequence"
(i.e., may be normalized into different strings by different
implementations), or PR29_STRINGPREP_ERROR if there was a
problem converting the string from UTF-8 to UCS-4.