#126 Do not open files to zip in exclusive mode

[Anonymous]

When a file to be zipped is in use by another process,
7zip (command-line version) abort.

- it should not abort on this error, but just skip the file
(you could make it an option ?)

- better yet, it should not try to open the file for
exclusive use. In shared mode, it could zip the file and
we could use it for backup purposes. (once again it
could be just an option).