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.
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.
Back to development version.
Update version numbers for 2.0.3 release.
Merge pull request #2345 from benbc/2.0-update-to-2.0.4

Update version numbers for 2.0.3 release.
Remove unnecessary checks when flattening ors and ands
Move expression reordering in Ors from query graph builder to ast rewriting
Merge pull request #2350 from systay/boolean-normalization

Move expression reordering in Ors from query graph builder to ast rewriting