HoudiniScene can use a default time during evaluation.

Added get/setDefaultTime methods, which provide a default cooking time for methods that do not accept time as an argument (e.g. hasObject or childNames). In a HoudiniScene which points at a SOP, it is necessary to use time in these methods. The default time will pass through to children automatically. If left unset, CHgetEvalTime() will be used
for these queries.
Setting default HoudiniScene time from SceneCache ROP.

This prevents double cooking when the current cache time does not match Houdini's current eval time.
Merge pull request #127 from andrewkaufman/houdiniSceneDefaultTime

HoudiniScene Default Time