* src/*: Introduce (basic) vim-style file locks. Does not allow vim to recover
our files, and doesn't yet support setting the file as modified; just lets a
vim user know we're editing a file. Commands line "-G" or "--locking", nanorc
option "locking". New functions src/files.c:do_lockfile(), write_lockfile(),
and delete_lockfile().
git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@4549 35c25a1d-7b9e-4130-9fde-d3aeb78583b8
bf88d27adc