Performed a more thorough audit of functions on Mac that require local pools. Added macros to these functions to hopefully reduce or eliminate leaks in apps that are threaded and perform GUI functions on secondary threads. _dw_pool_drain() is still available to drain the main thread pool, but enclosing the functions in these macros should reduce the objects accumulating in the thread's main pool.

# Set these here to change the version for all platforms
DW_MAJOR_VERSION=2
DW_MINOR_VERSION=2