All modules are always rebuilt when using M2 with a hierarchical structure

When using Maven2, the recommended directory structure for a multi-module build is hierarchical, e.g.:

• pom.xml (parent pom of all modules)
  • • module1
      +-- pom.xml
    • module2
      +-- pom.xml
      etc

When using such a structure with continuum, if a change is committed in module28, then EVERY module will be rebuilt: indeed the parent pom will be rebuilt because the change is "under" its scm tree, and all the other modules will therefore we rebuilt because of a "dependencies change" on the parent pom. This can easily multiply the build time by a factor of 10 or 20.

I have attached a patch. It considers that the parent has "changed" only if its pom.xml has changed. Not sure it is perfect, but it works for me (the patch has been tested (against continuum-1.1 and trunk). Feel free to rewrite or modify it as much as you like.