renaming of SHA1SUM in iso directory

[Keith G]

> This thread is just highlighting the problems with using extensions to
> disambiguate file-types.

No it's not.  This thread is primarily highlighting the fact that
SHA1SUM files, which relate to a specific FC version and arch, should
be named accordingly.  This IMO is a very good idea, because the name
"SHA1SUM" is meaningless when you have several different ISOs lying
around.  The ISO file itself is named according to the FC version
number and arch.  We don't simply call it "ISO".