[R-gui] GUI for require(package)!

But the reposTools / install.packages2() method can be slow
sometimes, because it searches multiple repositories for an R
package.  This may be fixed now, but in the past, I found that
(using the default options), it often searched the wrong
repository first, e.g. CRAN instead of Bioconductor.

It still does that.  It needs to get all the info from all of the
repositories (because you don't necessarily just want to get the first one
found if a package exists in multiple repositories - a later one in the
search path might be more appropriate), but right now it does that for
*every* package it is looking for.  I keep saying that I'm going to change
it to cache the repository metadata for the entire query but haven't ever
had a chance to do it.

and getBioC().  He also has a widgetInvoke package on
Bioconductor which could be of interest to Gtk fans on this
mailing list.

It is still quite rough, but "getting there".  It's another thing that
seems to get a burst of work done at infrequent intervals, unfortunately.

-J