Change collision logic in SceneObjectPart so land_collision will happen.

The previous logic would generate land_collision_start and land_collision_end
but would not generate the land_collision itself.
BulletSim: fixes for change linkset implementation of physical linksets.
BulletSim: add API and calls for spring constraint parameters.
BulletSim: add spring constraint to linkset constraint types.
BulletSim: complete linkage of spring constraint into linkset constraint.
BulletSim: add unmanaged and XNA functions for hinge, slider and spring constraints.
BulletSim: move linkset extension operations into BSPrimLinkable where they should be.
BulletSim: initial implementation of physChangeLinkFixed that resets a linkset's link back to a fixed, non-moving connection.
BulletSim: Linkset.Refresh() calls internal ScheduleRebuild() to recreate the linkset physics at next PostTaint time. Replace the existing calls to ScheduleRebuild to be calls to Refresh(). This allows external routines to make changes to parameters and then cause the linkset to rebuild.
BulletSim: add physChangeLinkSpring to change linkset link to be a spring constraint. Add implementation to create spring constraint. Send up property updates for linkset children at the end of flexible linkset links. The simulator probably doesn't do the right thing yet.
BulletSim: update C++ HACD parameters to values that handle enclosed hollow spaces better. This shouldn't affect many since this HACD routine is off by default.
BulletSim: add physChangeLinkParams to set individual parameters on link constraints. Not fully functional. Remove double definition of ExtendedPhysics parameters by having BulletSim reference the optional module (addition to prebuild.xml and usings).
BulletSim: change ExtendedPhysics constants to 'const' so they can be used as case variables in switch statements.
BulletSim: update DLLs and SOs with Bullet svn version 2644 (no major fixes) and with BulletSim implementing more of the constraint types and parameter settings.
BulletSim: add extended physics function physGetLinkType(linkNum). Add implementation of physChangeLinkParams() in BSLinksetConstraint.
BulletSim: adjust avatar capsule height calculation to be closer to defined SL heights. Correct BSParam avatar height defaults to be what's in OpenSimDefaults.ini.
BulletSim: Extension parameters passed through the classes made to pass just and array of objects rather than a mixture of parameters and array. Makes understanding and parsing what is being passed much easier.
BulletSim: add ID parameter to TaintedObject calls so logging will include LocalID of object which created the taint.
BulletSim: pass both root and child BSPhysObjects to Extension function. Update routines to use the new parameters list from above change.
BulletSim: add position and rotation update for child prim physics update events. Normally, physics engines do not return updates for child prims so, under normal operation, this code should never execute. Will only be used when using flexible linkset linkages.