Miscellaneous improvements to "jar".

[Alan Bateman]

Martin Buchholz wrote:
> :
>
> - using Path.moveTo is more likely to be atomic, so that
>   a concurrent process is less likely to find the jar being updated 
> missing.
> (Alan: is there a better way to do the common task of replacing a file
> with its transformed output?)
The moveTo method does have the ATOMIC_MOVE option for cases where you 
require it to be atomic but I don't think it is needed here. The 
transform into a second file and replacing the original seems fine, and 
probably the safest in that the original isn't trashed if something goes 
wrong.

-Alan.