(Make-)files that use mandir (and other data directory macros).

This patch solves a warning during configure, specifically:

...
config.status: creating Makefile.pre
config.status: WARNING:  ../Makefile.pre.in seems to ignore the --datarootdir setting
...

See also: <http://www.gnu.org/software/automake/manual/autoconf/Changed-Directory-Variables.html>