devel/got: update to 0.73

User-visible changes:
- got patch: use diff3 to merge changes if possible
- tog: alias C-b/C-f to scroll page back/forward with b/f
- tog: make SPACE page down in all views
- tog: allow prefixing movement keys with count modifier
- always show commit or tree IDs in diff header, in order to help 'got patch'
- tog: implement support for horizontal splitscreens
- switch 'tog diff' and 'tog blame' to Myers diff by default for speed
- make the diff algorithm used by 'tog diff' and 'tog blame' configurable
- got patch: handle mangled whitespace
- fix "imsg_add TREE_ENTRY: Result too large" error on i386
- create and verify tags signed by SSH keys
- tog: add C-g/backspace key map to abort compound commands
- rename got.conf(5) fetch-all-branches to fetch_all_branches for consistency
- rename got.conf(5) mirror-references to mirror_references for consistency