Cover template arguments and data member cases in the class2headers

procedure.
For the time being, seeking headers for return types of member
functions is disabled as it triggers an infinite recursion.
This will be ironed out once the whole "header on demand" mechanism
is up and running.
Trigger header parsing on demand during autoload

for the moment the parsing at library load, in RegisterModule is
not deactivated (it could be defining the env variable HEADER_PARSING_ON_DEMAND).
This is VERY TEMPORARY TO ALLOW hAVING BOTH SOLUTIONS SIMULTANEOUSLY.
The headers that would have been parsed could be visualised setting gDebug to 1.