[R] update.packages problem

[Terry Therneau]

I've updated to R-devel on my development machine and have lots of packages.  The 
update.packages() script ends up with 33 failures, all due to out-of-order reloading.  
That is, if package "abc" depends on package "xyz", then the reinstall of abc fails with a 
message that version of xyz is "built before R 3.0.0: please re-install it".

So I ran it a second time, and got 32 failures.  There should be a better way.