- 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

Fix some harmless bugs in a test.

Add some tests from PR 166463. Also make sure that all of the tests,
old and new, check the sign bits of both the remainder and the
quotient.

Test remainderl() and remquol() as well.

Fix a few of the tests so that correct implementations actually pass them.

A few simple regression tests for remainder(), remainderf(),
remquo(), and remquof().