Merge branch 'ab/fetch-tags-noclobber'

The rules used by "git push" and "git fetch" to determine if a ref can or cannot be updated were inconsistent; specifically, fetching to update existing tags were allowed even though tags are supposed to be unmoving anchoring points. "git fetch" was taught to forbid updates to existing tags without the "--force" option. This is a backward incompatible change but in a good way; it may still need to be treated carefully. * ab/fetch-tags-noclobber: fetch doc: correct grammar in --force docs push doc: add spacing between two words