Add examples for importing upstream sources
Add gbp buildpackage example

showing git-pbuilder invocation
Remove duplicate config files section

in the "gbp builpackage" man page
GitRepository.set_upstream_branch: Newer git wants a valid remote repo entry

so set one in the tests before trying to set the upstream branch.

Found with git 1.8.3.2
GitRepository.set_upstream_branch: don't try to set upstream twice

Move setting of the upstream branch out of the loop. This worked by
accident.
GitRepository.set_upstream_branch: Catch errors to set upstream branch
GitRepository.set_upstream_branch: use --set-upstream-to if available

since --set-upstream is deprecated.
Bump dephelper dependency
Document changes and release 0.6.2
--git-hooks doesn't take an argument