Support for inlining final methods with C++ back-end

Performance of many things in the X10 library depends on inlining final methods. Currently this isn't happening in C++ back-end. The following need to be done:

1. Ensure (at least final) method bodies are in .h files. (This is currently the case for generics, which is also the case for which inlining peformance is most critical, so for an initial implementation nothing needs to be done for this requirement).

2. Declare the method bodies with the "inline" keyword.

3. Use non-virtual calls o->C::m for calls to final methods.