Adding user defaults to plug popup menus when applicable.
Updated default build to use Cortex 9.0.0-a10
Moved Plug binding details to anonymous namespaces.
Fixed deadlocks if computes spawn their own threads.

We need to release the GIL on the thread which requests the compute, so that if the compute spawns threads, they can enter into Python.

The only example we have of this right now is the Instancer when getting the bounds, but I've fixed all the ValuePlug::getValue() bindings too for good measure.
Added GafferScene::PathMatcher::prune() method.

This is equivalent to removePath(), but additionally removes all descendant paths.
Added GafferScene::PathMatcher::isEmpty() method.

Fixes #1076.
Merge pull request #1091 from johnhaddon/getValueGILManagement

Fixed deadlocks if computes spawn their own threads
fixed SubTree sets problem where root path has no leading slash
Fixed PathMatcher::prune( std::string ).
Merge pull request #1096 from davidsminor/subtreeSets

fixed SubTree sets problem where root path has no leading slash
Merge pull request #1095 from johnhaddon/pathMatcherAPI

PathMatcher API additions
Added menu item for deleting CompoundDataPlugValueWidget children.

This allows items to be removed from CustomAttributes nodes and the like.

Fixes #1031.
Added SceneTestCase.assertBuiltInSetsComplete() method.

We were already checking that all objects referenced by sets do exist - this extends upon that by checking that all cameras, lights and coordinate systems that exist are referenced by the appropriate built in sets. The test has to be disabled for a couple of tests involving Alembic files, because we don't have a way of flagging cameras in those.
Added "isolate from" capability to GafferScene.Isolate node.

This causes the effects of isolation to be applied only below a certain location, making it easy to protect the rest of the scene from pruning.

Fixes #1057.
Updated Changes file.
Removed duplicate string->path code from SubTree.
 Removed duplicate string->path code from Constraint.
Optimised ScenePlug::stringToPath().

This gives an 88% reduction in runtime for a synthetic test of just that function, and a 7% reduction in total runtime for a scene benchmark using the Instancer.
Merge pull request #1099 from johnhaddon/compoundDataPlugDeleteUI

Added menu item for deleting CompoundDataPlugValueWidget children.
Merge pull request #1100 from johnhaddon/isolateFrom

Added "isolate from" capability to GafferScene.Isolate node