fixing collect_generation_garbage() complexity, doxygen, etc.

git-svn-id: https://gnunet.org/svn/gnunet@34426 140774ce-b5e7-0310-ab8b-a85725594a96
-do not do GC for each destroyed operation on client disconnect

git-svn-id: https://gnunet.org/svn/gnunet@34427 140774ce-b5e7-0310-ab8b-a85725594a96
-inline 

git-svn-id: https://gnunet.org/svn/gnunet@34428 140774ce-b5e7-0310-ab8b-a85725594a96
-indent

git-svn-id: https://gnunet.org/svn/gnunet@34429 140774ce-b5e7-0310-ab8b-a85725594a96
-indent

git-svn-id: https://gnunet.org/svn/gnunet@34430 140774ce-b5e7-0310-ab8b-a85725594a96