Add script for importing bits-and-pieces to Git.

Allows the user to import version history that is stored in bits and
pieces in the file system, for instance snapshots of old development
trees, or day-by-day backups. A configuration file is used to
describe the relationship between the different files and allow
describing branches and merges, as well as authorship and commit
messages.

Output is created in a format compatible with git-fast-import.

Full documentation is provided inline in perldoc format.

Signed-off-by: Peter Krefting <peter@softwolves.pp.se>
Signed-off-by: Junio C Hamano <gitster@pobox.com>