install-info will not install into non-existent dir file

[Gavin Smith]

I just hit a problem when trying to read the diff manual.  I ran
"info diff" and it wasn't found.  After struggling to check whether
I had the manual installed and finding that it was installed (as
/usr/share/info/diffutils.info.gz), and checking that that file had
a dir entry in it, I ran

$ sudo install-info /usr/share/info/diffutils.info.gz  /usr/share/info/dir

which appeared to work with no problems, but in fact the dir file had
not been created.

After doing "sudo touch /usr/share/info/dir" and re-running install-info,
I managed to run "info diff" successfully.

I suggest that install-info should create the file if it did
not exist already, or at the least give a warning about the file
not existing.