-return const, do not mangle const input

git-svn-id: https://gnunet.org/svn/gnunet@34435 140774ce-b5e7-0310-ab8b-a85725594a96
again, do not pass salt around, code cleanup, etc.

git-svn-id: https://gnunet.org/svn/gnunet@34436 140774ce-b5e7-0310-ab8b-a85725594a96
clean up internal set API, avoid copying context message needlessly

git-svn-id: https://gnunet.org/svn/gnunet@34437 140774ce-b5e7-0310-ab8b-a85725594a96