Update check_ref_format() function to reject ref names that:
* has a path component that begins with a ".", or
* has a double dots "..", or
* has ASCII control character, "~", "^", ":" or SP, anywhere, or
* ends with a "/".
Use it in 'git-checkout -b', 'git-branch', and 'git-tag' to make sure
that newly created refs are well-formed.