When adding a dependency, also add the dependency to the metadata hash.
Addresses part 1 of #3591. Prior to this fix, the regnerator only paid attention the mtime of the first dependency it checked, so for posts/pages with N multiple dependencies (i.e., every layout file used to render them), it continues to regenerate the post/page approximately N times, at which point it's seen all of the dependencies.
Two tests for the regenerator cache clearing changes:
1. Intrusively test that the regnerator.clear_cache actually clears the cache ( in test/test_regenerator.rb )
2. Test that incremental building regenerates files that have changed that previously were unchanged ( in test/test_site.rb )
Parker Moore
Nicholas Burlett
Alfred Xing