maint: Ignore generated version file

Commit 67a1de0d created a generated version file, and, in some
circumstances, also a temporary file.  Make sure 'git add .'
won't check them into the repository.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
