Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

- Move csup away from contrib/ and into usr.bin/. Software is no longer
contributed, and main development is happening in the FreeBSD repo.

Suggested by: joel

Merge support for CVSMode (aka. mirror mode) into csup. This means csup can now
fetch a complete CVS repository. Support for rsync update of regular files are
also included, but are not yet enabled. The change should not have an impact on
existing csup usage, as little of the existing code has changed.

- Update copyright.

- Fattrs are not used for rsync, so remove unused code.

- Refactor some parts of the code and increase code reuse.
- Fix a lot of style issues remaining and old debugging output.
- Update comments where needed.

- Fix build with GNU make.
- Fix compiler warnings and symbol overlaps.
- Don't build code that is not used yet.
- Fix types and format strings.

- Fix issues that prevented rsync support from working.

A few general bugfixes:
- Use internal xmalloc instead of malloc.
- Include missing header after warnings.
- Fix unneeded printouts.
- Fix a bug when checking the CO_NORSYNC flag.

- Implement rsync support in csup, which is chosen as a protocol for regular
files if the client supports it. The support is implemented with an API to
operate on files, calculating the rolling checksum and md5 checksum for the
blocks etc.
- Remove unneeded stream_filter_stop and stream_flush before stream_close.