[Rd] The Depends: field of a package is now used by library()

[Prof Brian Ripley]

In R-devel, the Depends: field in the DESCRIPTION file is now used by 
library() to load the named packages before the current package, and also 
to set up the environment to save images and prepare for lazy loading.

Would authors please use a minimally necessary set of packages in Depends, 
and put others in Suggests: -- the distinction is made in `Writing R 
Extensions'.  On the other hand, do include standard packages like
graphics, stats and utils if needed, as R can be run without these.
(For example, packages which define S4 methods for plot do depend on 
graphics and may fail if graphics is loaded after them.)

There is a little danger of cycles in dependencies if there are
unnecessary entries, and load time will be slowed (although with 
lazy-loading that is a much smaller penalty than it used to be).

This change should enable the installation procedure to be simplified for 
packages which save images -- you can probably omit both install.R and 
R_PROFILE.R and use fields in DESCRIPTION instead -- see `Writing R
Extensions'.  More details of recommended changes will appear on the 
developer site nearer release time.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595