NLTK: Quadratic-time DoS in PorterStemmer via long runs of 'y'

nltk.stem.PorterStemmer.stem -- a ubiquitous public API applied to arbitrary, often untrusted, tokens -- runs in On^2 time on a token containing a long run of the letter 'y', letting a single 20-50 KB token pin a CPU core CWE-407. Root cause isconsonantword, i was made iterative commit for 3633,...