Do not overwrite target unless source is modified

I thought MWAR-8 had fixed my issue but it seems to still exist. Correct me if I'm wrong but doing incremental builds with this war plugin is not possible. All the web app sources get overwritten regardless if they have been modified or not. Incremental build were possible in Maven 1 because it was ANT based. This version uses plexus FileUtils which overwrites without regard to if the target file exists or older than the source. Besides the time issue, overwriting the web.xml each time makes my context reload since the context runs on tomcat from the target location. I think this is a reasonable configuration but if there is a better way, let me know. Building inplace wars is not an option as it dirties the source.

If we are in agreement, I may be able to provide a patch.