Backport from master.
* src/editfns.c (rbc_quitcounter): Remove; the quitcounter
is now part of the context.
(EXTRA_CONTEXT_FIELDS): Remove unused member early_abort_tests.
Add jmp, quitcounter.
(Freplace_buffer_contents): Use setjmp/longjmp to recover from
a compareseq that runs too long. Omit unnecessary rarely_quit
call.
(buffer_chars_equal): Occasionally check for early abort and
longjmp out if so (Bug#43016).