format.c: Fix misuse of hash container function.

The supplied hash function to a container must be idempotent given the
object's key value to figure out which container bucket the object belongs
in.  Returning a random number or the current container count is not
idempotent.  The "computed hash" value doesn't help find the object later
in those cases.

* Fixed the format_list container to actually be a list since that is how
the container is used.  Conceptually, if more than 283 formats were added
to the format_list then odd things may have happened before the fix.
........

Merged revisions 415728 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@415729 f38db490-d61c-443f-a65b-d21fe96a405b