Merge branch 'issue683' into 1.6.x
fix duplicate @import detection and do not use ThreadLocal to avoid thread-safety issue
simplify rcursive detection
unregister mbean when filter is destroy to avoid memory leak. Create unit test.
update javadoc & small test update to make it pass with TravisCI
use assertEquals instead of org.hamcrest.MatcherAssert.Is which fails on TravisCI
update less4j version to 1.0.2
fix merge conflicts
add missing imports