Allowing .lscc files to be loaded
IECoreMaya fixed dag menu GL bug for sceneShapes
Fixing SceneCacheNode function signatures

Making scene() static since it doesn't use any member data or node parameters. Making get*() const.
renaiming "build" to "expand" and "clean" to "collapse" to match IECoreMaya naming
Separated Expand and Collapse functionality.

SceneCache OBJs now expand and collapse from separate functions (and buttons). The Expanded toggle marks the current state, and may be queried by external processes (such as a ROP) to determine if the user has fiddled with the underlying scene.
Changed behaviour of SubNetwork expansion to supress child objects.

This is necessary to ensure that objects are not expanded prior to children of the same level, providing a coherent definition for the expanded/collapsed state of each node.
Allowing custom attribute handlers to be registered with HoudiniScene
OBJ_SceneCacheTransform registers the LinkedScene attribute with HoudiniScene to represent unexpanded transforms as links.
LinkedScenes can now be written with the SceneCache ROP.

The ROP will now write attributes, the primary use of which is the link attribute for lscc files. Required wrapping the live HoudiniScene with a LinkedScene when writing non-linked files, to ensure full expansion of links.
Merge pull request #11 from valeriebernard/sceneShapeGLIssue

IECoreMaya fixed dag menu GL bug for sceneShapes
Merge pull request #12 from andrewkaufman/houdiniLinkedScenes

LinkedScenes in Houdini
Reorganized parameter creation for OBJ_SceneCache nodes to avoid horrible munging of PRM_Templates.
Added tagFilter to OBJ_SceneCacheTransform

The filter is used to control visibility when expanding nodes. Available tags are presented in the drop down menu.
Allowing custom tag handlers to be registered with HoudiniScene.

Note that this does not match exactly with IECoreMaya. This is a vector of tag handlers, rather than registered by specific tag name. This allows one handler to provide a list of tags all at once, which seems more in line with the
intention of SceneInterface::readTags().
OBJ_SceneCacheTransform registers a custom tag reader with HoudiniScene.

This simply translates the tags already existing in the scene file, and does not currently allow for live editing/addition of tags. Also, tags are not maintained when using FlatGeometry mode. In the future, tag addition and FlatGeometry tags may be made available using custom parameters and geometry prim vars.
Tags can now be written with the SceneCache ROP
IECoreMaya time connection from parent is preserved when expanding sceneShapes.
Merge pull request #14 from andrewkaufman/houdiniSceneTags

Scene Tags in Houdini
Merge pull request #16 from valeriebernard/sceneShapeTimeConnectionFix

IECoreMaya time connection from parent is preserved when expanding scene...