Added exception type.  The header provides macros to automate capturing
the scope, file, and line number at the point of a throw.
Added btException
Replaced implementation of btAssert with an exception.
Corrected order in the ctor init list.
Merge branch 'exception_support' of https://github.com/bgossage/bullet3 into iBullet3
Added btException
Added exception type.  The header provides macros to automate capturing
the scope, file, and line number at the point of a throw.
Replaced implementation of btAssert with an exception.
Added BT_USE_EXCEPTIONS macro to control when exceptions are used in asserts.
Added exception handling

Conflicts:
	src/LinearMath/btScalar.h