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.

This iteration fixes the most recent issues, including operation without implying -f/--no-reuse-delta.