(PUP-1186) Ignore PAX header in tar unpacking

Prior to this commit if you installed a puppet module built on a platform with
a tar implementation that adds PAX headers and your platform didn't have a native
tar implementation (Windows), the module would contain junk PaxHeader directories.

This is due to the default POSIX behavior programmed in to minitar (the ruby tar
implementation used for platforms with out native tar) for an unknown typeflag,
such as those used in PAX headers, is to treat it as a regular file and extract it.

This commit adds a pre-scan step to our use of minitar for unpacking that finds
all the files with standard typeflags (0-7) and then only unpacks those, thus ignoring
any Pax typeflags like 'x' or 'g'.