Raise WARNS to 6:

Raise WARNS to 6:
- Declare variables and parameters 'static' and 'const' as needed.

Also:
- Bump FreeBSD CVS id's (date.c:1.47 (imp); extern.h 1.XX (markm))
  to indicate that these files are functionally identical;
- Remove unnecessary casts;
- Apply some style(9).

Submitted-by: Sarunas Vancevicius <svan_at_redbrick_dot_dcu_dot_ie>