bug#29495: Remember last file where a variable was changed

[積丹尼 Dan Jacobson]

Maybe these

    max-specpdl-size is a variable defined in ‘C source code’.
    Its value is 1335
    Original value was 1300

      This variable may be risky if used as a file-local variable.

    Documentation:
    Limit on number of Lisp variable bindings and ‘unwind-protect’s.
    If Lisp code tries to increase the total number past this amount,
    an error is signaled.
    You can safely use a value considerably larger than the default value,
    if that proves inconveniently small.  However, if you increase it too far,
    Emacs could run out of memory trying to make the stack bigger.
    Note that this limit may be silently increased by the debugger
    if ‘debug-on-error’ or ‘debug-on-quit’ is set.

    You can customize this variable.

should not only keep a record that a value was changed, but also at
least the name of the last file that changed it. (As I can't seem to
find where it got changed.)