In case you guyz care:
The solution is not properly correct. If I setup an eclipse Luna SR1 with latest m2e, STS and sonar-ide then I end up with two bundles for slf4j:
This is breaking m2e with this error:
java.lang.IncompatibleClassChangeError: Class ch.qos.logback.classic.LoggerContext does not implement the requested interface org.slf4j.ILoggerFactory
Removing slf4j.api_1.7.2.jar fixes m2e but causes
org.osgi.framework.BundleException: Could not resolve module: org.sonar.ide.eclipse.wsclient 
Unresolved requirement: Require-Bundle: slf4j.api; bundle-version="1.6.6"
The problem is that plugin vendors like sonar-ide, m2e or STS have to talk with each other.
However sometimes they just do not care and end-users are left in trouble: