git fetcher unpack optimization V2

From: Yu Ke <[email protected]>

This is the remaining patches of last fetcher patch pull, including
- optimize git unpack method to use git local clone
- not to create the source tree mirror tar ball

With Richar and Bruce's comment, this patch is revised accordingly, the major chagnes compared with V1 is:
- use git local clone instead of git repo copy to save disk space

it has been tested with "bitbake poky-image-sato" with empty DL_DIR

Pull URL: git://git.pokylinux.org/poky-contrib.git
Branch: kyu3/git-unpack-2
Browse: http://git.pokylinux.org/cgit.cgi/poky-contrib/log/?h=kyu3/git-unpack-2

Thanks,
Yu Ke <[email protected]>
---

Yu Ke (3):
bb.fetch2: add git unpack
kernel-yocto.bbclass: adjust the git dir to fit with git unpack git.py: remove the source tree tar ball

 bitbake/lib/bb/fetch2/git.py      |   66 ++++++++++--------------------------
 meta/classes/kernel-yocto.bbclass |    4 +-
 2 files changed, 21 insertions(+), 49 deletions(-)