v4l2

1) update handler
2) video source resolution change
3) control of second v4l2 instance creation
 ua - ua_hungup_other_calls fixed to have worked with multiple accounts

	modified:   src/ua.c
silent calls are terminated after timeout

	modified:   include/baresip.h
	modified:   src/config.c
	modified:   src/core.h
	modified:   src/stream.c
 "Check" unit test system integration

	modified:   Makefile
	new file:   tests/main.c
	new file:   tests/tests.mk