bug#7246: Please add a customizable variable to disable generating lock (symlink) files

[Ken Hori]

Please add customizable variables to either:

1. Disable generating lock (symlink) files of the form:
  .#<filename> -> <user>@<host>.<pid>:<boot_time>
  (See: lock_file_1 in filelock.c)

or

2. Let the user specify a directory all lock symlinks are saved under.

This is to address the existing problem (bug) where Emacs often
leaves .#<filename> symlinks unlinked and so covers the
filesystem with worthless dirt, which piles up en masse as time
passes by.