Setting up a work environment:

First, clone the git repository (which does not contain source tarballs) and
then sync the source tree on top of it.
The git exclude list will ensure that "git status" will not report the source
tarballs as 'untracked'.

$ git clone git://taper.alienbase.nl/bootstrap.git
$ cd bootstrap
$ rsync -av  rsync://taper.alienbase.nl/mirrors/alienarm/bootstrap/ .

This is how the git exclude file should look like in your local git clone:
$ cat bootstrap/.git/info/exclude 
# ------ 8< -----------------------------------------------------------------
# git ls-files --others --exclude-from=.git/info/exclude
# Lines that start with '#' are comments.
# For a project mostly in C, the following would be a good set of
# exclude patterns (uncomment them if you want to use them):
# *.[oa]
# *~
*~
*.tar.bz2
*.tar.gz
*.tar.xz
*.t?z
!diff.?z*
!patch.?z*
# ------ 8< -----------------------------------------------------------------