Support multi-region OAR files

Merged ArchiveWriteRequestPreparation.cs and ArchiveWriteRequestExecution.cs. This simplifies the code, and it's faster to write each scene to the archive as it's found rather than all at once at the end.
Rename ArchiveWriteRequestPreparatio nto ArchiveWriteRequest since after the multi-OAR patch there is now only one class that handles this operation.

Adapation of 0004-Renamed-ArchiveWriteRequestPreparation-to-ArchiveWri.patch in http://opensimulator.org/mantis/view.php?id=6105
since that did not directly apply
Added unit tests for multi-region OARs
For FlotsamAssetCache, always update access times of cached scene assets before looking for files to expire.

This is to resolve a problem where an asset marked as local but not temporary but still used in the scene would be removed.
The timed expiry scan no longer tries to refetch assets from the scene that are not currently in the cache - this is not helpful since it just drags a lot of data into the cache that may never be referenced.
This removes the DeepScanBeforePurge option since setting this to false will introduce the above problem.  This previously had a default of true.
Add basic asset connector tests to check behaviour for normal, local and temporary assets.

Make AssetServiceConnector return more useful data on failure, such as what DLL it was trying to load
Allow LocalAssetServiceConnector.GetData() to work without a cache present, as works for the other lasc Get* methods.
BulletSim:  Way too many changes in one commit.
Many changes to BSDynamic for readability and commentary.
Linkset hacking for vehicles: don't over mass the root prim.
Add parameter for link constraint solver iterations.
Correct uses of timestep in timescale calculations for vehicles.
Reorganize code/logic for making objects static and dynamic for readability
    and use of API2.
Changed most calls in BSPrim to use API2 calls (the new way).
Avatars do not generate default Bullet collision events but do call up
    to the simulator for every avatar. Reduces overhead.
Objects added to collision list only if they are processing collisions.
    Reduces overhead especially for large numbers of avatars.
Generalize call for water height to GetWaterHeightAtXYZ().
Catch and correct exception getting terrain height when out of bounds.
Correct race condition in Terrain Manager where creation wasn't at taint-time.
Add API calls for constructing compound shapes.
Move NeedsMeshing() logic into object class.
Reorganize logic for object meshing to reduce rebuilding of meshs/hulls.
BulletSim: Add 'IsNativeShape2' call
BulletSim: remove unused NeedsMeshing() code from BSScene.
BulletSim: Add calls to linkset class when object going static or dynamic.
Reset center of mass on an object when going dynamic.
BulletSim: set all linkset objects center of mass to the whole linkset's center of mass
BulletSim: Remove calculation and passing of unused collied object type.
Fix collision code to properly sense mega-region children regions as terrain.
When setting an object physical, reset all the physical properties (friction, ...).
BulletSim: remove timeStep parameter from calls for vehicle parameter setting. There is no reason these should be using the simulation time interval for parameter calculation.
BulletSim: another attempt at computing physics FPS correctly.
BulletSim: add the debugging routine DumpRigidBody2() to API2.
BulletSim: some debugging prints in BSPrim for tracking changes in linkset children.
BulletSim: update DLLs and SOs and remove some debugging code.
More on HG2.0: added the possibility of controlling the appearance that avies use to visit other grids. Not as good as I wanted, but good enough. Unfortunately we can't switch the appearance from under the avie without getting into a lot of weirdnesses because appearance is viewer-controlled. So instead, when this control is on, I'm disallowing HG-TP unless the user is wearing an allowed HG appearance -- the user gets a warning and needs to switch appearance. WARNING: I'm still not committing the config vars because this is still not ready for ppl to test.
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim
HG2.0: Generalized the allowed HG appearances to be more than 1.