check mechanism. For example, we can't expect external implementations such as
Mina, jetty, jboss to follow SLF4J's release schedule. We just can't.
This commit changes the version check policy to become elective. The FAQ includes an entry explaining
the logic.
- added a new module called "integration" for testing interactions between
various SLF4J versions. This module uses Ant and relies on Ant's flexibility
in providing different classpaths to various tasks (this is much harder to do
with Maven). The Ant build file is still invoked by Maven. Thus, integration tests
are run at build time.