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

Remove unused variable. Shorten the path to WARNS=6 compliance.

Don't add integers to void pointers.

Clean up error handling in libstand filesystem code to be more consistent:
- bzipfs and gzipfs now properly return errno values directly from their
read routines rather than returning -1.
- missing errno values on error returns for the seek routines on almost
all filesystems were added.
- fstat() now returns -1 if an error occurs rather than ignoring it.
- nfs's readdir() routine now reports valid errno values if an error or
EOF occurs rather than EPERM (It was just returning 0 for success and
1 for failure).
- nullfs used the wrong semantics for every function besides close() and
seek(). Getting it right for close() appears to be an accident at that.
- read() for buffered files no longer returns 0 (EOF) if an error occurs,
but returns -1 instead.

- Move the code to try to open a single chunk file and prompt for the
associated floppy if needed into a static split_openfile() function.
- Use this function in splitfs_open() to open the first chunk rather
than using open() directly. This allows the first chunk to be located
on a different disk than the actual foo.split file.

Whitespace tweaks to make indentation consistent within this file and even
within a single function.

Kill debugging printf() slipped into my last commit.

Noticed by: jhb
Hall of shame entry: sobomax

(forced)

Splitfs is subject of:

MFC after: 2 weeks

Add splitfs vfs layer into libstand, which allows loading big kernels and
modules split across several physical medias. Following is how it works:

The splitfs code, when asked to open "foo" looks for a file "foo.split"
which is a text file containing a list of filenames and media names, e.g.

foo.aa "Kernel floppy 1"
foo.ab "Kernel floppy 2"
foo.ac "Kernel and modules floppy"

For each file segment, the process is:

- try to open the file
- prompt "Insert the disk labelled <whatever> and press any key..."
- try to open the file
- return error if file could not be located

RE team is free to use this feature in the upcoming 5.0-DP1.

Reviewed by: msmith, dcs