Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Give fstest a more unique name: pjdfstest.
It is released from time to time and used outside FreeBSD, so it is good to
have a name one can google.

MFp4: - When new object is created, it's group ID can be set to process'
effective group ID or to group ID of its parent directory.
- Add some comments from POSIX.
- Verify that after successful O_TRUNC open, size is equal to 0.

Add 3436 file system regression tests in 184 files.
Almost all regression tests are based on very flexible fstest tool.
They verify correctness (POSIX conformance) of almost all file
system-related system calls.

The motivation behind this work is my ZFS port and POSIX, who doesn't
provide free test suites.

Runs on: FreeBSD/UFS, FreeBSD/ZFS, Solaris/UFS, Solaris/ZFS

To try it out:

# cd fstest
# make
# find tests/* -type d | xargs prove