stop assuming inf2cat is on the path; the signing code should call it
specifying path explicitly
add giturl option to override giturl in config file
remove reference repositories support; it isn't much use now that clones
do not need to be repeated on each interactive build
simplify git handling. You may specify branch or tag but not
both. There's some logging around the git operations and some checking code.
add repositories.txt files for openxt platform and windows. Add a script
to do a windows build in one go.