Severity: wishlist

Please see the attached patch.

I've been able to measure around 10% better performance in the few cases
I looked into.  Here's an example:

    (benchmark-run 1000
      (seq-filter (lambda (n) (bufferp n))
                  (number-sequence 0 100000)))
    => (69.007736 333 47.018879999999996)

    (benchmark-run 1000
      (seq-filter #'bufferp
                  (number-sequence 0 100000)))
    => (61.541616 333 47.673137)