JXR Report isn't generated for tests unless sources exist

The JXR report is not generated for tests unless sources exist. I can submit a patch if necessary but the fix is very simple.

1. In plugin.jelly the maven-jxr-plugin:register goal nests <j:if> statements such that test sources report won't be registered unless sources report is registered. Un-nesting these ifs solves half the problem.

2. Exactly the same issue in the maven-jxr-plugin:report goal. Un-nesting the ifs means that you can generate a test report even if sources don't exist.

Motivation:

I have separated out my XP style acceptance tests into a separate sub-project. This sub-project tests the built and deployed system as a whole and doesn't have it's own source.

Matt.