This allows the git repository to be moved while git-annex is running in
it, with fewer problems.
On Windows, this avoids some of the problems with the absurdly small
MAX_PATH of 260 bytes. In particular, git-annex repositories should
work in deeper/longer directory structures than before. See
http://git-annex.branchable.com/bugs/__34__git-annex:_direct:_1_failed__34___on_Windows/
There are several possible ways this change could break git-annex:
1. If it changes its working directory while it's running, that would
be Bad News. Good news everyone! git-annex never does so. It would also
break thread safety, so all such things were stomped out long ago.
2. parentDir "." -> "" which is not a valid path. I had to fix one
instace of this, and I should probably wipe all calls to parentDir out
of the git-annex code base; it was never a good idea.
3. Things like relPathDirToFile require absolute input paths,
and code assumes that the git repo path is absolute and passes it to it
as-is. In the case of relPathDirToFile, I converted it to not make
this assumption.
Currently, the test suite has 16 failures.
It's ok to probe every time for git-branch remove because that's
run quite rarely. For git-checkattr, it's run only once, when
starting the --batch mode, and so again the overhead is pretty minimal.
This leaves 2 places where the build version is still used.
git merge might be interactive or fail if one skews, and --no-gpg-sign
might not be pased, or might be passed to a git that doesn't understand it
if the other skews. It seems a little expensive to check the git version
each time these are used.
This doesn't seem likely to cause many problems, at least compared with
check-attr hanging on skew.
In the case where a remote of the bare repo has a fetch = configuration,
refs/remotes/origin/master will exist, and so the merge code path tried to
run in the bare repo.
