Tries to get missing package files from host
Checks that paths in tar archive are sane
Makes shell_escape() less aggressive
Makes shared files even more shared

Moves reprozip.tracer.common to reprozip.common
Puts back unused (config-writing) code in reprounzip.common
Removes _pytracer.FILE_* (use copies on common.py instead)
Various fixes
Writes select_box()
Only unpacks other_files in Vagrant box
WIP
More WIP on vagrant
WIP