PBGitRepository: Correctly indicate bare/non-bare repos
This addresses an issue with non-bare repos which had no core.bare
variable in the config. The isBareRepository-function would work
on the full fileURL (pointing to the .git subdir), which in turn would
indicate a bare repo (this is what git rev-parse --is-bare-repository
returns in .git, and the opposite is true for the superdir).
We work around by using the working-dir for a repo (and directly
indicating a bare repo if there is no workdir). The only issue remaining
is the case of a bare repo manually set to "core.bare = false".
Signed-off-by: Johannes Gilger <heipei@hackvalue.de>