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

Introducing memcchr(3).

It seems two of the file system drivers we have in the tree, namely ufs
and ext3, use a function called `skpc()'. The meaning of this function
does not seem to be documented in FreeBSD, but it turns out one needs to
be a VAX programmer to understand what it does.

SPKC is an instruction on the VAX that does the opposite of memchr(). It
searches for the non-equal character. Add a new function called
memcchr() to the tree that has the following advantages over skpc():

- It has a name that makes more sense than skpc(). Just like strcspn()
matches the complement of strspn(), memcchr() is the complement of
memchr().

- It is faster than skpc(). Similar to our strlen() in libc, it compares
entire words, instead of single bytes. It seems that for this routine
this yields a sixfold performance increase on amd64.

- It has a man page.