Merge branch 'jk/fetch-quick-tag-following'

When fetching from a remote that has many tags that are irrelevant
to branches we are following, we used to waste way too many cycles
when checking if the object pointed at by a tag (that we are not
going to fetch!) exists in our repository too carefully.

* jk/fetch-quick-tag-following:
  fetch: use "quick" has_sha1_file for tag following

diff --cc builtin/fetch.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc sha1_file.c
Simple merge