Path to the Git repository directory can be overriden by using the '$GIT_DIR'
environment variable. This patch improves detection of Git repository by using
'git-rev-parse', which respects '$GIT_DIR' environment variable, instead of just
checking the existence of '.git' directory.

Signed-off-by: Vasilis Tsiligiannis <acinonyx@openwrt.gr>

SVN-Revision: 49165

Git internals are referenced by .git which isn't necessarily a
directory. It may also be a file that references the actual .git
directory using the gitdir directive.

If .git is assumed to be a directory the build will not be able to get
the correct version when openwrt is included as a git submodule because
when used as a submodule .git will actually be a file referencing to a
subdirectory in the parent's git dir.

When the correct version is not detected some image generation tools
will fail because the OpenWrt string will be 'OpenWrtunknown' which is
too long for some header formats.

Signed-off-by: Felix Kaechele <heffer@fedoraproject.org>

SVN-Revision: 44452

SVN-Revision: 28604

getver: don't use "-r COMMITTED" arg which needs network access to the repository, use the "Last Changed Rev:" line instead

SVN-Revision: 17864

getver: get svn rev from last commit so that we have consistent revision numbers between git and svn

SVN-Revision: 17781

SVN-Revision: 17432

SVN-Revision: 12380

SVN-Revision: 10059

clean up openwrt version handling, use a separate script that is executed at the beginning of the build process, fix revision checking with git

SVN-Revision: 9723