GRADLE-2825 - disable the duplicate file deprecation warning.

If no strategy has been set and there are duplicates, notification is sent to the info logger.
Remove duplicated test.
Reduced the log level of a message that summarises the utilisation of a worker thread. Remved some dead code.
Reduced log level of the message that summarises the in-memory dependency metadata cache usage.
Reduced log level for messages that inform about the file lock contention events.
Make the incubating feature message more formal.

(cherry picked from commit b5b8b7b)
GRADLE-2821 - Handle reporting on test tasks that ran no tests.

If all test tasks to be reported on have no results, then the test report task is skipped.
Improve/correct the docs for duplicate handling.
Corrected issue number linked in release notes
formatting.
GRADLE-2829 - fix JacocoMerge functionality.
GRADLE-2836 - make class generation thread safe.
Merge branch 'release'

Conflicts:
	subprojects/core/src/main/groovy/org/gradle/api/file/CopySpec.java
	subprojects/core/src/main/groovy/org/gradle/api/internal/file/copy/DuplicateHandlingCopySpecVisitor.java
	subprojects/core/src/main/groovy/org/gradle/cache/internal/DefaultFileLockManager.java
	subprojects/core/src/main/groovy/org/gradle/util/SingleMessageLogger.java
	subprojects/docs/src/docs/release/notes.md
	subprojects/plugins/src/main/groovy/org/gradle/api/internal/tasks/testing/junit/result/AggregateTestResultsProvider.java
	subprojects/plugins/src/main/groovy/org/gradle/api/internal/tasks/testing/junit/result/BinaryResultBackedTestResultsProvider.java
	subprojects/plugins/src/main/groovy/org/gradle/api/internal/tasks/testing/junit/result/TestReportDataCollector.java
	subprojects/plugins/src/main/groovy/org/gradle/api/internal/tasks/testing/junit/result/TestResultsProvider.java
	subprojects/plugins/src/test/groovy/org/gradle/api/internal/tasks/testing/junit/result/TestReportDataCollectorSpec.groovy
	subprojects/plugins/src/test/groovy/org/gradle/api/internal/tasks/testing/junit/result/TestResultSerializerTest.groovy
	subprojects/plugins/src/testFixtures/groovy/org/gradle/api/internal/tasks/testing/BuildableTestResultsProvider.groovy