Add runtime support for OpenGL tracing

This is an extension of #1653: Add runtime support for OpenGL debugging.

The idea is to add a trace call to every delegate in the GL wrappers when tracing is enabled:

Trace.Write(StringFormat("Foo({0}, ..., {n}) -> ", param_0, ... param_n));
// call native function pointer
Trace.WriteLine(return_value or "null");

The main difficulty here is finding out the values of every parameter passed by the user, plus the return value (if it exists). Tracing.zip contains a simplified GL-like binding for experimentation.

Anyone familiar with runtime code generation willing to lend a hand?