Doc: Bring groovy versions back into alignment

Minor change to userguide to bring groovy versions back into alignment.
First stab at implementing finaliser tasks. Dependencies of finaliser tasks are for now ignored.
Also handle dependencies of finaliser tasks
Make build dashboard task a finaliser for reporting tasks
Run finaliser tasks as soon as possible
Mock a task method to fix some tests
Docs for finaliser task and the missing setter for finalisedBy
Fix setter for finalisedBy and add a test for it.
Use US spelling for 'finalize'
Add finalizedBy edges to task graph so that finalizer dependencies are traversed only once
More extensive integration tests for finalizer tasks
Documentation fix: your are -> you are
GRADLE-2171: Added DuplicatesStrategy allowing duplicate
files (based on their path) to be included or excluded, by
default for an entire copy operation or on a per-file basis

- duplicatesStrategy field to FileCopyDetails so individual files
  can specify their own strategy for handling duplicates

- add duplicatesStrategy field to CopySpec so that an entire copy
  spec can specify the default strategy (this can be overridden
  for some or all files)

- add CopySpec.matching and .notMatching convenience
  methods. These let the user modify a group of FileCopyDetails
  simultaneously. Motivated by setting a duplicatesStrategy for
  eg, "META-INF/**/*.xml" but is generally useful

- added CopySpec.duplicatesPriority that determines precedence
  among CopySpecs when a duplicate file is to be
  excluded. Plugins can set a higher duplicatesPriority for some
  specs (eg, Jar.manifest and Jar.metaInf), but this property is
  not currently user-settable.
GRADLE-2171 Improve documentation for DuplicatesStrategy-related method calls and add to DSL documentation
Added support for bintray's jcenter repository
Merge from master
GRADLE-2171 Restore imports lost while merging conflicts
GRADLE-2171 Change case of DuplicatesStrategy enumeration so that Gradle can automatically coerce strings to enum types.
Reduce number of task graph traversals, remove implicit mustRunAfter for finalizer tasks.
GRADLE-2171 Remove duplicate priority logic, expect specifications to be ordered based on their precedence. Right now the Ear test for deploymentDescriptor precedence is failing