Refactored cross sphere line tracking and added a unittest to verify correct operation

src/systemcmds/tests/tests_main.c

@@ -90,6 +90,7 @@ const struct {
 	/* external tests */
 	{"commander",		commander_tests_main,	0},
 	{"controllib",		controllib_test_main,	0},
+	{"mc_pos_control",	mc_pos_control_tests_main,	0},
 	//{"mavlink",		mavlink_tests_main,	0}, // TODO: fix mavlink_tests
 	{"sf0x",		sf0x_tests_main,	0},
 #ifndef __PX4_DARWIN

src/systemcmds/tests/tests_main.h

@@ -92,6 +92,7 @@ extern int controllib_test_main(int argc, char *argv[]);
 extern int uorb_tests_main(int argc, char *argv[]);
 extern int rc_tests_main(int argc, char *argv[]);
 extern int sf0x_tests_main(int argc, char *argv[]);
+extern int mc_pos_control_tests_main(int argc, char *argv[]);
 
 
 __END_DECLS