- 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

Hide expected error output so the 'prove -r' results are easy to read.

Update the number of reported tests to keep prove(1) happy.

Correct the "move file from directory to existing directory" test for
cross-device moves.

Portability improvements to investigate behavior of other OSs.
Now works under Solaris and Linux.

Add more tests. All rename(2)-based tests now succeed.
The performance of the cross-device equivalents is under investigation.

Verify that the moved source is no longer there.

Regression tests for upcoming makeup of mv.
Case 20 corresponds to PR bin/118367.