Fixes download_file() failing when using its cache
Makes 'script.sh' files executable

For the 'directory' and 'chroot' unpackers, these files should probably
be executable.
Restores shared files
Adds buildpkgs.py script
Fixes 'directory' script.sh having two PATHs

The new computed PATH variable was appended instead of replacing the
PATH in the original environment.
PATH for 'directory' goes in and out of dir

If the original PATH was '/usr/bin:/bin', we would previously use
'mydir/usr/bin:mydir/bin'. We now use
'mydir/usr/bin:mydir/bin:/usr/bin:/bin'.
Adds big warning if using Python 2.6 (or before)
Bumps reprounzip version to 0.3.2
Merge branch 'v0.3' into 'master'

Conflicts:
	CHANGELOG.md
	reprounzip/reprounzip/unpackers/default.py
Bumps version to 0.4