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