Debugging builds of R GUI on the nightly pages

I have added a new build target named "Debug" to the R GUI - the 
corresponding nightly binaries can be obtained from the nightly build 
pages as usual:
http://www.rosuda.org/R/nightly/
The debugging build should be used when reporting error/crashes as it 
prints more debugging informations on such occasions. The binary is not 
optimized, but since R library used by the GUI is still the same, there 
should be no noticeable slowdown compared to the regular build in 
(which means that you may as well use the debug build when testing 
"nightlies").

I'm trying to track down some errors reported to this list earlier - 
some are addressed in the current build, others should follow later 
this week.

Cheers,
Simon