Change how replay programs are identified, from filename to sym export

* Instead of checking on the filename, we look for a specially named
  exported symbol somewhere in a module that's already loaded.
* This allows us to mark the python module as a replay program, so if
  it's loaded into the python interpreter it will be able to use the
  replay API.

renderdoccmd/renderdoccmd.cpp

@@ -729,6 +729,8 @@ struct CapAltBitCommand : public Command
   }
 };
 
+REPLAY_PROGRAM_MARKER()
+
 int renderdoccmd(const GlobalEnvironment &env, std::vector<std::string> &argv)
 {
   try
@@ -898,4 +900,4 @@ int renderdoccmd(const GlobalEnvironment &env, int argc, char **c_argv)
     argv[i] = c_argv[i];
 
   return renderdoccmd(env, argv);
-}
+}