Bug fix: preventing a Computation result to be recomputed everytime it's queried because of unmatching hash.

Added a test showing the situation where it can happen: if the computation result is registered artificially and the hash of the given object does not match the real computation result, then it would never update the internal computation hash and would force the computation every time.
Added gl:primitive:selectable flag
Added workaround for 3delight 11.0 in IECoreRI::Renderer::worldEnd.

3delight 11.0.0 now generates a new RtContextHandle in worldEnd and whisks the other one away onto a background thread to do rerendering, so we have to talk to the new one instead. New approach tests OK in 11.0.0 and 10.0.173. Note that one test (light edits) is still failing in 11.0.0, but this so far at least appears unrelated to the context changes.
Added failing test for LinkedScene
Adjusting SceneCache read time in Houdini.

We need to adjust the time we read SceneCaches inside Houdini because Houdini treats time starting at Frame 1, while SceneInterfaces treat time starting at Frame 0. Note that we should really be adjusting time by 1/fps used at cache time, but we don't have access to that, so we currently assume that Houdini's current frame rate is representative.
HoudiniScene uses SceneInterface standards for time.

Calls to HoudiniScene will expect SceneInterface time (starting from Frame 0), and will internally adjust when querying Houdini.
SceneCache ROP adjusts time before querying HoudiniScene
Correcting HoudiniScene customAttributeReaders so the ReadFn accounts for time.

Now all links written from Houdini are time re-mapped.
Merge pull request #130 from danieldresser/drawSelectedFlag

Added gl:primitive:selectable flag
Merge pull request #131 from johnhaddon/delight11Fixes

Added workaround for 3delight 11.0 in IECoreRI::Renderer::worldEnd.
defaultTime is now private and renamed to adjustedDefaultTime
Merge pull request #132 from andrewkaufman/timeOffset

Fixing SceneInterface Time in Houdini
Adding warning message when the stored hash differs from the computed Object's hash.
Merge pull request #121 from ldmoser/recomputationBug

Bug fix: preventing a Computation result to be recomputed everytime
Updated Changes and bumped version to 8.0.0a19.
Fixed IE buildAll script for internal wrapper changes.
Fixing the unit test in LinkedSceneTest.py ( testLinkBoundTransformMismatch ).

When bbox samples were being accumulated for each call to accumulateBoxSamples(), we were not considering the case that there could be samples already registered and located earlier in time.
The solution adopted was to use the first new sample bbox and use it to enlarge any known bbox that came prior in time.
Merge pull request #133 from ldmoser/preExtrapolationBBox

Fixing the unit test in LinkedSceneTest.py ( testLinkBoundTransformMismatch )
Reorganizing parameters on SceneCache OBJs.

Standard OBJ parms are now visible. This required re-jigging things so our new folders are in the same tab layout (switcher) as the originals. Since the original transform parms do not function, the Transform folder is hidden by default.

This causes a strange bug which is fixed by the next commit.
Overriding getIndirect() to avoid parm caching errors.

This cryptic virtual function is used (internally by Houdini) to cache parameter indices, so that parm lookup by name is done only once. This seems to only affect the SceneCache OBJs because they're the only nodes which add their own parameters before base class parameters.

This solves the bug mentioned in the previous commit. All tests pass again.