Fixing bug in multi-threaded reads in StreamIndexedIO.

The problem was due to DirectoryNode instances created after expanding sub-indexes which had unsorted child nodes. That could cause sorting later by calls to findChild().
Fixed bug from maintenance branch merge
Merge pull request #322 from valeriebernard/transformOpBugFix

Fixed bug from maintenance branch merge
Update Changes
SceneCache writeBound() change

Bounding boxes explicitly written using writeBound() can now be dilated by child bounds, rather than totally overriding them
enabled read/write of extra children at link locations
simplified SceneCache::WriterImplementation::accumulateBoxSamples, added some unit tests
installing 3delight's iePython.so procedural to a versioned python directory
Merge pull request #324 from davidsminor/versionedRiPythonProcedural

installing 3delight's iePython.so procedural to a versioned python directory
Merge pull request #323 from davidsminor/linkedSceneExtraChildren

Linked scene extra children
Restricting Houdini version installs at Image Engine.
updated changes, bumped version to 9.0.0-a4
updated IEBuild version in postCoreHoudiniInstall
restricted nuke versions at image engine
Merge pull request #326 from davidsminor/restrictNukeVersions

restricted nuke versions at image engine
Merge pull request #325 from davidsminor/postCorehoudiniInstallFix

updated IEBuild version in postCoreHoudiniInstall
Renamed MayaScene to LiveScene
Renamed HoudiniScene to LiveScene
LinkedScene::hash now takes extra children at links into account
removed outdated comment