git: tag is not fetched

[Georges Racinet]

While working on a tag will fetch and checkout the commit this tag points at, it does not fetch the tag ref itself.
Hence for instance if we have this

  git http://some.where.git myaddon v1.2

with the tag pointing at commit 12deadbeef,

the recipe will indeed retrieve 12deadbeef, but the pointer v1.2 -> 12deadbeef will not be created.
Hence this will fail :

   git checkout v1.2

In particular, all reverts done subsequently by the recipe will fail

[Georges Racinet (gracinet)]

fixed the failing checkout example in issue description