Miscellaneous patches on github

[Nigel Stewart]

Hello all,

Cross-posting here on the mailing list of additional opinions and eyeballs.

1. Resolve C4267 MS compiler warnings
https://github.com/apitrace/apitrace/pull/156
Use explicit c-casting to appease the MS compiler.

2. Support for Mac OS X 10.5 Leopard
https://github.com/apitrace/apitrace/pull/157
CGLShareGroupObj and IOSurfaceRef were added 10.6 SDK.
Still builds for 10.5 with some modest workarounds.

3. Replace dynamic_cast with virtual functions
https://github.com/apitrace/apitrace/pull/158
apitrace can be built with without RTTI if dynamic_cast is avoided.

These originate from our effort to integrate apitrace into Regal as a
dispatch layer.  These patches bring the projects into closer
alignment.
https://github.com/p3/regal

- Nigel