Asterisk crash when unloading cdr_radius/cel_radius.

Asterisk crash when unloading cdr_radius/cel_radius.

The rc_openlog() API call is passed a string that is used by openlog() to
format log messages.  The openlog() does not copy the string it just keeps
a pointer to it.  When the module is unloaded, the string is gone from
memory.  Depending upon module load order and if the other module then has
an error, a crash happens.

* Pass rc_openlog() a strdup'd string with the understanding that there
will be a small memory leak if the cdr_radius/cel_radius modules are
unloaded.

* Call rc_destroy() to free the rc handle memory when the module is
unloaded.

JIRA AST-483
JIRA SWP-3062

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@321926 65c4cc65-6c06-0410-ace0-fbb531ad65f3