wrong installation places for docs

[Bernd Warken]

The actual groff CVS version installs the documents to the wrong places
according to the FHS (filesystem hierarchy standard).

info: should be /usr/local/share/info, i.e. $datadir/info, not $prefix/info
man: should be /usr/local/share/man, i.e. $datadir/man, not $prefix/man

doc: the doc top directory is ok, but is it necessary to install all
documents in a versioned subdirectory.  I think it should be enough to
override previous version, just like man and info do.

Bernd Warken