Merge branch 'jc/merge-tag-object' into maint

"git merge $(git rev-parse v1.8.2)" behaved quite differently from
"git merge v1.8.2", as if v1.8.2 were written as v1.8.2^0 and did
not pay much attention to the annotated tag payload.  Make the code
notice the type of the tag object, in addition to the dwim_ref()
based classification the current code uses (i.e. the name appears in
refs/tags/) to decide when to special case merging of tags.

* jc/merge-tag-object:
  t6200: test message for merging of an annotated tag
  t6200: use test_config/test_unconfig
  merge: a random object may not necssarily be a commit

diff --cc builtin/merge.c
Simple merge