A new packer for .tar.gz files (MIME type application/x-gzip) has been
implemented, including unit tests.
This packer is intended for use during backup/restore only and is not
otherwise exposed in the user interface at present. However, it is
supposed to follow the (ancient) POSIX .tar standard; files created
with this packer will open in GNU tar.
There are restrictions in support corresponding to the POSIX standard:
- Non-ASCII filenames are not supported.
- Very long file/path names are not supported.
- Individual files within the .tar may not be more than 8GB.
Some of these limitations might need to be addressed in future changes
if the packer were to be used in areas other than backup/restore.
