use DIRECTLY_UPDATE_VELOCITY_DURING_SOLVER_ITERATIONS by default for now,
until we find the issue with some failing test cases in btMultiBody
fix a crashing issue in MyMultiBodyCreator.cpp (uninitialized variable)
disable excessive debug printf in URDF2Bullet
remove targetdir from all libraries in premake, so it is much easier to create a separate folder for all binary+lib
transmit the serialized btMultiBody data back from server to client, after the server loads a URDF file. This includes base+link+joint names
tweak the serialization routines, so it is easier to skip pointers and to serialize directly to a shared memory buffer
also tweak the serialization code to allow to process data without 'DNA' schema data (assuming file-DNA = memory DNA)
add importer support for FIXED_CONSTRAINT_TYPE, to be replaced by btGeneric6DofSpring2Constraint
btFixedConstraint now derives from btGeneric6DofSpring2Constraint
