[Rd] Suggestion: Allow packages to add additional information to sessionInfo()

[Henrik Bengtsson]

Hi,

sessionInfo() has been proven really useful, but you still often have
to ask for additional information in order to help troubleshooting.
For instance, for troubleshooting the aroma.affymetrix, it is very
helpful to know what the current working directory is, for other
packages certain system environment variables might be useful and so
on.

One solution could be to provide support for hook functions of
sessionInfo(), which package then can register and append to the
'sessionInfo' list structure.  Does this make sense?

/Henrik