Add share/info/*/dir to those files in STAGEDIR to ignore when checking
for orphans, i.e., files in STAGEDIR that are not covered by plist.

This is a follow-up to revision 484628 after which texinfo files are
now installed into ${PREFIX}/share/info. (A file "dir" is then created
and maintained by the tooling.)

Approved by: portmgr (antoine)