1. The license header is technically not valid if it doesn't have a
copyright signature.
2. The COPYING file has been updated with the different licenses used in
the project.
3. The full GPLv2 header in each file annoys me.
This code is useful for more things than just the packfile handling
code. Factor it out so it can be reused.
Signed-off-by: Carlos Martín Nieto <carlos@cmartin.tk>