Work around git-annex breakage.

Seems new versions of git annex just bail out when run in a "bare"
repository, (at least when git config core.bare return true).

Problem is, you can create work trees from bare repositories and then
the result is not really "bare" even though git config core.bare will
return "true".  Since site deployment does this, and then tries to run
git annex, we get pointless failures.

Simple enough to just manually set core.bare to false when running
git annex, which seems sufficient to make things work again.