[git-buildpackage] Would it be possible for pristine-tar to not be an absolute path?

[Nish Aravamudan]

Hello,

I am currently using gbp in a snap for `git-ubuntu`, a tool similar to
dgit for doing Ubuntu source package work. The snap contains all its
dependencies, including pristine-tar at paths within the snap (which I
ensure are in PATH when my tool runs), but gbp has a hard-coded path
to pristine-tar:

gbp/pkg/pristinetar.py:
...
class PristineTar(Command):
    """The pristine-tar branch in a git repository"""
    cmd = '/usr/bin/pristine-tar'

Is that strictly necessary for the way Command works? Would it be
possible to allow the cli (since it may not be override-able
otherwise) to specify where pristine-tar lives rather than it being
hardcoded?

Thanks,
Nish