git-fetch: follow tag only when tracking remote branch.

git-fetch: follow tag only when tracking remote branch.

Unless --no-tags flag was given, git-fetch tried to always
follow remote tags that point at the commits we picked up.

It is not very useful to pick up tags from remote unless storing
the fetched branch head in a local tracking branch.  This is
especially true if the fetch is done to merge the remote branch
into our current branch as one-shot basis (i.e. "please pull"),
and is even harmful if the remote repository has many irrelevant
tags.

This proposed update disables the automated tag following unless
we are storing the a fetched branch head in a local tracking
branch.

Signed-off-by: Junio C Hamano <junkio@cox.net>