reportproxies optimized

The subroutine name of the proxy is now retrieved from the call stack of
the first require instead of the previous heuristic that was looking for
/^sub / in the source file.
Note that this is still not perfect as for closures named with different
names (exemple:
   Sub::Name::subname('sub'.rand) => sub { require $module };
) we will only get the first name. We should document this limitation.