- 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

Add a sendfile regression test for transmit length > file size.

This test identified the issue fixed in FreeBSD-SA-13:11.sendfile.

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

Allow to specify path to a file we want to test with sendfile(2).
This allows to specify selected file system and not only /tmp/.

Update the sendfile regression test so that it outputs results in the
TAP format.
Add a checksum to verify that the data hasn't been corrupted between
being read from disk and being received.

Approved by: rrs (mentor)

o Correct a comment: a test file size is a four pages not three.

Test sending 0 bytes.

Fix length calculation.

Valid error codes for err() and errx() are 1..255.
The correct format specifier for ssize_t is %zd.

Add more tests to verify last sendfile(2) breakage: test sending more
than a page size and nbytes=0.

Add a basic regression test for sendfile() over TCP, which sends varying
lengths of headers and data and makes sure it receives about the right
number of bytes.