Add some constness to avoid some warnings.
Remove use register keyword.
Deal with missing/unneeded extern/prototypes.
Some minor type changes/casts to avoid warnings.
Reviewed by: md5
Write status information to stdout instead of stderr.
Exit status when an error occurs musn't be 1, that is reserved for
indicating that messages are disabled.
These changes bring mesg(1) up to SUSv3 conformance.
Reviewed by: mike
