1. For fns like comint-postoutput-scroll-to-bottom on comint-output-filter-functions...

1.  For fns like comint-postoutput-scroll-to-bottom on comint-output-filter-functions, don't count back using the length of STRING, as previous fns may have changed the buffer.  Count from process-mark.
2.  Don't bind file-name-handler-alist, it can break dir tracking.
3.  Expand ^ in input only at boi.
4.  Use new comint-file-name-regexp as source of valid chars in filenames.