We were using the libopus directory itself rather than a file within
it as a makefile target.  This is a bad idea as make will see the
target as updated whenever files are created in or removed from the
directory.  Since running configure creates and removes files, the
target will always appear dirty.

The effect was that when mod_opus was enabled in FS make would always
cause libopus to be reconfigured.

We'll target instead the configure file in libopus as that's the first
thing we need anyway.

sofia_glue_get_url_from_contact to strdup the value so before
overwriting the value signal to sofia that we have finished with the
raw header.

sip_header_as_string returns new memory alloc'd on the nua_handle's memory pool. This memory would not be freed until
the handle was destroyed. Since there is no usage of the call-info header after it is added to the event as a header value,
we should make sure to both su_free the sofia returned string, but also more cleanly create the event header value to reduce a strdup.

CID:1210789 Make return value of a function available from the another calling function.  Also add a small status check.

CID: 1214223-1214230 If sent an invalid registration authentication header with multiple params of the same name, then only use the first of the params instead of leaking memory

CID:1024250 Dereference before null check. CID:1024251 Dereference before null check, we don't need tto check these, as they are already used above in all cases

CID:1214196 Dereference null return value, if we hit this condition, something very bad has happened, we should never have the private not set if we get to the hangup hook, log error instead of crashing