- normalize for() loops to navigate through variables,

  removing replicated var = var->next;
- remove a potential infinite loop and document the problem
- remove useless checks and document why
- mark XXX a possible bug (to be investigated)
- use ast_strlen_zero() instead of expanding it inline
- fix indentation in one place   
- replace a nested 'if' with '&&'



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@20223 65c4cc65-6c06-0410-ace0-fbb531ad65f3