Fixes race that can cause duplicate writes in XaLogicalLog

There is a possible window where a transaction may fail to flush
 the log buffer (for example, during a commit) and even though
 it will set the KernelHealth to notOk, another thread can still
 come and try to flush the same contents again (say, by attempting
 a commit of its own tx). This can cause the log to be unrecoverable.
 This commit fixes this issue by introducing checks to KernelHealth
 before any write happens to the log's underlying file.
Merge pull request #2326 from digitalstain/1.9-fix-damaged-log-writes

Fixes race that can cause duplicate writes in XaLogicalLog
added script to detect unauthorized contributors
testing anonymous contributions: adding a dot
testing anonymous commits: changed a comment
testing anonymous commits: removed a newline in text
Merge pull request #2330 from lassewesth/anoncontrib

Testing anonymous contributions
support for using Iterable<Node> as start points for traversals

Enabling nested traversals (or run traversals based on a Cypher result) without the need to first consume the first traversal. TraversalDescription accepts to use Iterable<Nodes> for start nodes.
 Internally we already had support for Iterable<Node> instead of Node.... but we didn't expose it.
Logging performance optimizations:
* Added custom Jetty logger that caches isDebugEnabled
* Changed LogbackService to cache isDebugEnabled
* Added isDebugEnabled check before toString() in HighPerformanceCache
Only add security filter if there are security rules
License header fix
Debug cache is now no longer static.
Added comment that the request log needs to decorate all other handlers.
Merge branch '1.9-maint' into 1.9-merge

Conflicts:
	community/kernel/src/main/java/org/neo4j/kernel/impl/transaction/xaframework/XaLogicalLog.java
	community/kernel/src/test/java/org/neo4j/kernel/impl/transaction/xaframework/XaLogicalLogTest.java
2.0.3 changelogs
Merge pull request #2339 from jakewins/1.9-merge

1.9 merge
Tagging for version 2.0.3
Handle pruning old format logs, Fixes #2265
Handle backup when no logs are present on target db.
Added +UNWIND+ to Cypher

UNWIND can be used to transform a collection into individual rows.
Back to development version.