[Rd] Rgui bug in Windows: leftover download dialog (PR#7964)

[murdoch@stats.uwo.ca]

In Windows, if a download is interrupted (by switching to the console 
window and hitting ESC), the download status dialog can be left 
onscreen, with no apparent way to get rid of it (other than stopping and 
restarting R).

To duplicate:

Run this:

a <- available.packages()
download.packages(a, 'c:/temp')

Then, during a particularly long download, switch to the console window 
and hit ESC.

This affects R-devel, as well as 2.1.1.

Duncan Murdoch