buildrelease.py: use git root instead of cwd if no fresh repo
buildrelease.py: use git root instead of cwd if no fresh repo

This way the script works even if called from a subdirectory of the
repository.

ipso/ADOdb,azghanvi/ADOdb,ipso/ADOdb,andrewnicols/ADOdb,azghanvi/ADOdb,andrewnicols/ADOdb,pyscht/ADOdb,paulproteus/ADOdb,paulproteus/ADOdb,pyscht/ADOdb