fix doc typo
streamline some paths for equality and hashing

Cuts about 1/3 of the time for a string-hashing microbenchmark
provided by Pedro Ramos:

 #lang racket
 (define alphabet "abcdefghijklmnopqrstuvwxyz")
 (define (random-word n)
   (build-string n (lambda (x) (string-ref alphabet (random 26)))))
 (define words (for/list ([k 1000000])
                 (random-word 3)))
 (define d (make-hash))
 (time (for ([w (in-list words)])
         (if (hash-has-key? d w)
             (hash-set! d w (add1 (hash-ref d w)))
             (hash-set! d w 1))))
filesystem-change-evt: report inotify_init() error correctly