+ create function cdr_get_tv to replace several duplicated

+ create function cdr_get_tv to replace several duplicated
  instances of the same code to generate a time entry in
  raw or localtime format;

+ create functions check_post() and check_start() to check whether
  a record has been already posted or started, replacing
  several duplicated instances of the same code;

+ localize some variables;

+ normalize some for() loops

Especially the former two changes should make the code a lot
more consistent and easier to read.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@17878 65c4cc65-6c06-0410-ace0-fbb531ad65f3