Get same instance id across all message tests to prevent receiving messages from a previous test because of forking.

give more time to create account (due to DNS SRV request that are sometimes not responded very fast)

This reverts commit e2609f96.

This reverts commit 9eca8962.

reuse same sip.instance in account manager of tester

change the way payload type numbers are assigned, so that an application can support more payload type than the RTP profile table allows to contain.
Compliance with RFC3264 (offer answer model) is improved, by reusing numbers in case of reINVITEs.
Fix memory leaks
Move offer/answer related tests into a new test suite.

- Add the function linphone_address_equal().
- The comparison of two proxy config addresses now returns one of these three values: equal, weak-equal or different.
- If the new proxy config identity is equal to the previous one, a call to linphone_proxy_config_done() does not
unregister and does not delete the sal op. If it's weak-equal the sal op is destroyed but the unregister is not
done. Finally, if it's different the unregister is performed and the sal op is destroyed.

This reverts commit b61302f9.

tester automatically creates unique accounts on flexisip server before running tests. This allows several developer to run the test suite simultaneously !