- Fix protocol regex.
- Truncate repeated leading slashes in file paths.
- Make drive letter support platform-independent.
- Drop the hostname if a drive letter is parsed.
- Fix drive letter normalization and basing.
- Allow basing over the host.
- Fix same-protocol basing.
- Remove Windows UNC path support.
- Reverts #6418. This is non-standard. Wouldn't be too much of a problem but it
makes other parts of the spec hard to realize.
