git-p4: add support for large file systems

git-p4: add support for large file systems

Perforce repositories can contain large (binary) files. Migrating these
repositories to Git generates very large local clones. External storage
systems such as Git LFS [1], Git Fat [2], Git Media [3], git-annex [4]
try to address this problem.

Add a generic mechanism to detect large files based on extension,
uncompressed size, and/or compressed size.

[1] https://git-lfs.github.com/
[2] https://github.com/jedbrown/git-fat
[3] https://github.com/alebedev/git-media
[4] https://git-annex.branchable.com/

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Conflicts:
	Documentation/git-p4.txt
	git-p4.py
Signed-off-by: Junio C Hamano <gitster@pobox.com>