This shell script creates a docker image for running the gitian-build.py
script, to avoid version incompatibilities. The builds may be signed
automatically after manually reviewing the build hashes.
Only docker.io and apt-cacher-ng are required to be installed on the
host. The MacOSX SDK should also be present in this directory if Mac
builds are desired. A container named "gitrun" is used to launch
the builds, and all output will reside in this container as well.
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