Fix fileio.c infloops on circular lists

Fix fileio.c infloops on circular lists

Fix infinite loops in fileio.c when a circular list is the
value of after_insert_file_functions,
buffer-auto-save-file-format, buffer-file-format, or
write-region-annotate-functions.
* src/fileio.c (Finsert_file_contents, build_annotations):
Use FOR_EACH_TAIL to avoid infloop on circular lists.
(build_annotations): Use an EMACS_INT, not an int, to count
nesting level.
* test/src/fileio-tests.el:
(fileio-tests--circular-after-insert-file-functions): New test.