acc: free extra attributes for db, radius and diameter

- after the commit to allocate memory for extra attributes, only log
  accounting was freeing the memory
- reported by Luca M.

(cherry picked from commit 3afb2ea88fea4765a73e37f24b40dff8c8487122)
core: keep the password only if the user part is set

- a report by Timo Klecker

(cherry picked from commit 8c3d167b63096d3b465c53aca92ee18c5255188c)
exec: use proper header field iterator to print env variables

- issue introduced with the patch for shellshock
- reported by and credits for troubleshooting to Kristian Kielhofner

(cherry picked from commit 8855e3e7fcece4ca2ab33e1f9c54b15831152400)