[PATCH v4] git-archive: Add new option "--output" to write archive to a file instead of stdout.

Hi,

Patch attached as MIME.

Patch highlights:
1. Remove duplicated tests
1.1 Tests are present on t0024.
1.2 Introduced some comments in t5000 to make it easy to read.
2. Removed close(2) and comments from archive.c
3. Rewrote commit message.
4. Signed off.

Cheers!