Ensure the reference name is well-formed.
Valid reference names must follow one of two patterns:
- Top-level names must contain only capital letters and underscores,
and must begin and end with a letter. (e.g. "HEAD", "ORIG_HEAD").
- Names prefixed with "refs/" can be almost anything. You must avoid
the characters '~', '^', ':', '
', '?', '[', and '*', and the
sequences ".." and "@{" which have special meaning to revparse.
