Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Put parentheses in the right place.

Noted by: jilles@
Broken by: me. :-(

Build tr(1) with WARNS=6.

Revert most part of 200420 as requested, as more review and polish is
needed.

Remove unneeded header includes from usr.bin/ except contributed code.

Tested with: make universe

Splay the left and right subtrees on min - 1 and max + 1, respectively,
before trying to coalesce. Forgetting to splay caused us to miss many
opportunities for coalescing.

Initialize cs_invert to "false" in new csets.

Add support for multibyte characters. The challenge here was to use
data structures that scale better with large character sets, instead of
arrays indexed by character value:
- Sets of characters to delete/squeeze are stored in a new "cset" structure,
which is implemented as a splay tree of extents. This structure has the
ability to store character classes (ala wctype(3)), but this is not
currently fully utilized.
- Mappings between characters are stored in a new "cmap" structure, which
is also a splay tree.
- The parser no longer builds arrays containing all the characters in a
particular class; instead, next() determines them on-the-fly using
nextwctype(3).