Support test command line option

[danielbodart]

Basically would print out exactly the same output but doesn't actually do any downloading,

Useful for Make integration with a little shell parsing

Originally requested by @npryce

https://twitter.com/natpryce/status/452923665387372545

[sl4mmy]

I think a -n|--dry-run option would be helpful, so +2 for @joewalnes and I! :)

Even better would be to spit out the full list of dependencies in Makefile syntax suitable for inclusion like gcc -M|-MM. Is that too specific to just one build tool for ShavenMaven, though?

[npryce]

Any format that is easy to transform with UNIX filters would work.

But I'd consider that a different use case than "dry run". I'd expect dry run to be the same as a normal run but doesn't actually modify the filesystem. So, the tool would print the human readable output rather than machine readable data.