Several bug fixes today and got caught up on most recent messages. Backlog
is 157.

The most significant one prevents git-annex from reading in the whole
content of a large git object when it wants to check if it's an annex
symlink. In several situations where large files were committed to git, or
staged, git-annex could do a lot of work, and use a lot of memory and maybe
crash. Fixed by checking the size of an object before asking 
`git cat-file` for its content.

Also a couple of improvements around versions and upgrading. IIRC git-annex
used to only support one repository version at a time, but this was changed
to support V6 as an optional upgrade from V5, and so the supported versions
became a list. Since V3 repositories are identical to V5 other than the
version, I added it to the supported version list, and any V3 repos out
there can be used without upgading. Particularly useful if they're on
read-only media.

And, there was a bug in the automatic upgrading of a remote that caused it
to be upgraded all the way to V6. Now it will only be upgraded to V5.

Today's work was sponsored by Jake Vosloo on
[Patreon](https://patreon.com/joeyh/).
