- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Handle some expression regressions.
Explicitly use GNU cpp for preprocessing.
Remove explicit debugging code.
Change some variable names to be less confusing.
Improve some comments.
Improve indentation.

PR: 162211
168785
MFC after: 2 weeks

Make clang happier by removing unused assignments.

On request of joel@:

- Remove the 3rd clause of the UC Berkeley copyrighted files.
- For the files added copyrighted by me, move the "All rights
reserved" to the next line.

Long awaited update to the calendar system:

- Repeating events which span multiple years (because of -A, -B or
just the three days before the end of the year).

- Support for lunar events (full moon, new moon) and solar events
(equinox and solstice, chinese new year). Because of this, the
options -U (UTC offset) and -l (longitude) are available to
compensate if reality doesn't match the calculated values.

MFC after: 1 month