Starting with a change to ensure that ast_verbose() preserves ABI compatibility

Starting with a change to ensure that ast_verbose() preserves ABI compatibility
in 1.6.1 (as compared to 1.6.0 and versions of 1.4), this change also
deprecates the use of Asterisk with FreeBSD 4, given the central use of va_copy
in core functions.  va_copy() is C99, anyway, and we already require C99 for
other purposes, so this isn't really a big change anyway.  This change also
simplifies some of the core ast_str_* functions.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@157639 65c4cc65-6c06-0410-ace0-fbb531ad65f3