do not export the tzlock and the list head, and introduce a new method,

ast_walk_indications(), to walk through the list of indications.
The new method returns an unlocked record, which is no different from the
behaviour of other existing methods in indications.c
(i.e. they all need to be fixed, with refcounts or some similar
method).

Note that ast_walk_indications() uses the pointer argument only as a
search key, so its implementation is completely safe.

In turn, this change allows the removal of AST_MUTEX_DEFINE_EXPORTED.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@16532 65c4cc65-6c06-0410-ace0-fbb531ad65f3