Merge branch 'mg/maint-tag-rfc1991'

* mg/maint-tag-rfc1991:
tag: recognize rfc1991 signatures
tag: factor out sig detection for tag display
tag: factor out sig detection for body edits
verify-tag: factor out signature detection
t/t7004-tag: test handling of rfc1991 signatures

diff --cc builtin/tag.c
Simple merge

diff --cc builtin/verify-tag.c
Simple merge

diff --cc t/t7004-tag.sh
Simple merge