The .linphonerc file was not created at the first launch of Linphone.
The realpath function fails and returns NULL when passing a path which points on
an empty file.

revert changes made into linphone_gtk_update_call_buttons() as they are totally breaking the management of start_call and add_call buttons.

fix regression in mkv file player test, introduced by 3f86b78b (wav and mkv file swapped)

proxy.c: we must also UNREGISTER when being in state RegistrationInProgress so that even if registration is pending we unregister properly

Clear pending tcp/tls address of record in case of network change. Very useful for legacy SIP server with  no sip instance support and limited number of air.

proxy config: modify linphone_proxy_config_get_contact and add linphone_proxy_config_get_identity_address returning LinphoneAddress and move all documentation to linphone_proxy_config.h

lpconfig.c: use lp_realpath stub beacuse windows does not support/implement realpath and use proper string allocator