OAK-2302 - Simplify query debugging with MDC

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1642119 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'upstream-trunk' into OAK-2077
OAK-2077: Improve the resilence of the OrderedIndex for dangling links

completed refactoring to a generic createContent()
OAK-2077: Improve the resilence of the OrderedIndex for dangling links

refactored to a generic truncate()
OAK-2077: Improve the resilence of the OrderedIndex for dangling links

refactored to a generic filter()
OAK-2077: Improve the resilence of the OrderedIndex for dangling links

refactored to a generic assertion method
OAK-2077: Improve the resilence of the OrderedIndex for dangling links

code polishing