Fix 2004/gavin/{kernel,fs.tar} commit

Landon pointed out some issues that I missed (thank you Landon .. I was
very tired and I hope that I got everything this time) in commit
4b0a2cb64a:

0.  The make clobber rule removes the git files 2004/gavin/kernel and
    2004/gavin/fs.tar.

1.  The 2004/gavin/fs.tar file contains the file "README.md" which, when
    untarred, will overwrite the git file 2004/gavin/README.md.

2.  The 2004/gavin/fs.tar file contains the file "gavin.c" which, when
    untarred, will overwrite the git file 2004/gavin/gavin.c.

3.  The 2004/gavin/fs.tar file is a tar file that could be related with
    just checking in the 3 files "prim", "sh" and "vi".

and I discovered another issue too namely that the tarball had the wrong
version of gavin.c in it as well (prior to the fix for clang).

Now the tarball is in the img/ subdirectory and the tarball contents (is
that tar ? :-) ) looks like:

    $ tar ft img/fs.tar
    fs/
    fs/gavin.c
    fs/vi
    fs/README.md
    fs/sh
    fs/prim

I added to the todo.md file that this file should be verified to match
the contents of 2004/gavin and I gave a command to do to test this - at
the end of working on this entry or maybe better yet right before this
repo is to be folded back into the winner repo.

Updated .gitignore so that the files that are in img/fs.tar are not
added to the repo. The tarball is not meant to be extracted anyway but
rather copied to a disk for usage of the entry. It will be extracted to
verify that the contents match that of the entry itself (2004/gavin
directory).

2004/gavin/.gitignore

@@ -3,3 +3,6 @@ sh
 vi
 gavin.o
 fs/
+img/README.md
+img/gavin.c
+img/prim

2004/gavin/README.md

@@ -66,7 +66,8 @@ Press and hold any key.
 
 [Yusuke Endoh](/winners.html#Yusuke_Endoh)  provided the `kernel` and `fs.tar`
 files which can be used if you cannot normally use this entry. Instead of
-generating the files just use the files provided.
+generating the files just use the files provided, found under the [img/](img/)
+directory.
 
 Thank you Yusuke!
 

todo.md

@@ -1,5 +1,5 @@
 # A todo list of known things to check and/or do
-*Last updated: Wed  3 May 2023 14:57:29 UTC*
+*Last updated: Fri 19 May 2023 09:39:17 UTC*
 
 More things will likely be added over time and as items are done they _should
 be_ removed from the list IF AND ONLY IF (!!) we are certain it is done (many
@@ -55,3 +55,12 @@ only the years through 1986 are done. This should not take much time but I
 This will likely not be updated until after it's done (and when I remember to
 remove it - I expect that when I go for it I'll do it in one sitting or maybe a
 few sittings with a few brief breaks).
+
+- Verify that [2004/gavin](2004/gavin/)'s [img/fs.tar](2004/gavin/img/fs.tar)
+contains the same version of files as under [2004/gavin](2004/gavin/) itself.
+This should be verifiable by extracting the tarball in the entry's [img/](img/)
+subdirectory and then typing the below from the entry's main directory
+([2004/gavin](2004/gavin)), making sure no output is displayed:
+
+	diff -r . img/fs|grep -v 'Only in'
+