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

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

More -Wmissing-variable-declarations fixes.

In addition to adding missing `static' keywords:
- bin/dd: Pull in `extern.h' to guarantee consistency with source file.
- libexec/rpc.rusersd: Move shared globals into an extern.h.
- libexec/talkd: Move `debug' and `hostname' into extern.h.
- usr.bin/cksum: Put counters in extern.h, as they are used by ckdist/mtree.
- usr.bin/m4: Move `end_result' into extern.h.
- usr.sbin/services_mkdb: Move shared globals into an extern.h.

MFp4 @27667: WARNS=5 cleanup on i386.
Remove the unused FILE\ *tf from print_mesg args, and the
bogus passing in of an uninitialised FILE* for it.

Call a timeval 'now' instead of 'clock' due to shadowing.

Remove a nested localtime declaration.

Make the delete invite argument match the ID type, u_int32_t.

Use const for pointers to const items.

Cast to long where printing as such.

Include netinet/in.h for htonl/htons.

Reviewed by: imp

Fix minor disorder in functions declared in extern.h

o Move externs to extern.h
o Use new-style prototypes exclusively rather than the old foo() style.
o Use new-style function definitions.
o remove register
o make functions passed to signal have the right signature.
o do minor const poisoning.