setlocalversion: Ignote SCMs above the linux source tree

Dan McGee <dpmcgee@gmail.com> writes:
> Note that when in git, you get the appended "+" sign. If
> LOCALVERSION_AUTO is set, you will get something like
> "eee-gb01b08c-dirty" (whereas the copy of the tree in /tmp still
> returns "eee"). It doesn't matter whether the working tree is dirty or
> clean.
>
> Is there a way to disable this? I'm building from a clean tarball that
> just happens to be unpacked inside a git repository. One would think
> setting LOCALVERSION_AUTO to false would do it, but no such luck...

Fix this by checking if the kernel source tree is the root of the git or
hg repository. No fix for svn: If the kernel source is not tracked in
the svn repository, it works as expected, otherwise determining the
'repository root' is not really a defined task.

Reported-and-tested-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>