[PATCH 0/8] git-repack --max-pack-size

The three most common ways of making large packfiles
are git-fast-import, the first git-repack, or git-repack -a.
The first already supports a "--max-pack-size=N" option,
which limits the resulting packfiles to N megabytes.
This patchset adds the same option, with the same
behavior, to git-repack to handle the other two cases.

After reviewing others' comments,  this latest patchset
touches 2/3 fewer files and 1/6 fewer lines,  and
introduces no behavior not seen elsewhere in git.