.. in the face of using `git am` to apply patches.
We set `GIT_COMMITTER_NAME` and `GIT_COMMITTER_EMAIL` to fixed
values and provide a `gitam_mkpkg` function that passes
`--committer-date-is-author-date`
The means we can generate packages with the same, correct sha1
without needing to mess about with `git reset` (and thus getting
the old sha1 before our patches were applied).
Also, removed the `-j1` from make since it doesn't seem to be
needed anymore. Perhaps upstream fixed a race condition?
